Tagged Exercise

How Exercise Changes Our Blood

While we exercise, we raise and lower the levels of hundreds of molecules in our bloodstreams that are related to our metabolic health, even if we work out for only a few minutes, according to a complex and encouraging new study of the molecular effects of being active. The study, which involved more than 1,000 men and women, adds to growing evidence that exercise improves our health in large part by transforming the numbers and types of cells inside of us.

There is at this point, of course, no reasonable debate about whether exercise is good for us. It is. Countless studies show that people who are active are less likely than more-sedentary people to develop or die from a host of health problems, including heart disease, diabetes, dementia, cancer, obesity and many others. Active people also tend to live longer and feel happier.

But we still know surprisingly little about just how exercise changes us for the better. What are the many, interconnected biological steps and transmutations that allow a walk today to add to our life span decades from now?

That question has been driving considerable interest recently in research looking at exercise “omics” — the study of all of the molecules in our blood or other tissues that are part of a particular biological process. Genomics, for instance, quantifies the many, many molecules involved in genetic activities. Proteomics does the same for proteins, microbiomics for the multiple contents of our microbiomes and metabolomics for molecules related to metabolic processes. (There can be overlap between various ’omics, obviously.)

Understanding how exercise affects the levels of the various molecules within us is important, because these changes are likely to be the preliminary step in a complex cascade of further biological actions that contribute to better health. Increase some molecules, decrease others, and you jump-start inter-organ messaging, gene expression and other processes that subsequently alter how we make and use insulin, burn or store fat, respond to cholesterol and so on.

A number of important recent studies have delved into the ’omics of exercise, including a fascinating experiment showing that a short workout rapidly changes the levels of 9,815 molecules in people’s bloodstreams. But that study, like most other examinations of exercise and ’omics, involved relatively few volunteers — 36, in that case — and did not link molecular changes with subsequent health outcomes.

So, for the new study, which was published in September in Circulation, researchers at Massachusetts General Hospital in Boston and other institutions decided to up the number of exercisers whose ’omics would be parsed and also try to find connections between the ’omics data and later health.

Conveniently, they had access to a large group of potential volunteers among men and women already enrolled in the long-term Framingham Heart Study, which is overseen primarily by researchers at Massachusetts General Hospital. The scientists now asked 411 middle-aged volunteers enrolled in the study to visit the lab and exercise, by pedaling to exhaustion on a stationary bicycle. Most riders’ efforts lasted for a little less than 12 minutes. The researchers drew blood before the ride and afterward, within about a minute of when, worn out, the cyclists quit.

The scientists then ran the blood samples through a mass spectrometer, a machine that counts and quantifies molecules. The researchers focused on metabolites, which are molecules related to metabolic processes. The label “metabolite” is somewhat arbitrary, but for this study, the researchers focused mostly on molecules that could affect people’s insulin, fat burning, cholesterol, blood sugar and other aspects of cellular fueling.

They found plenty. Of 588 metabolites checked, the levels of more than 80 percent generally grew or dropped during the short rides. To reinforce those findings, the scientists repeated the experiment with another 783 Framingham volunteers, checking their blood before and after exercise for changes in about 200 of the molecules that had been most altered in the first group. Again, these metabolites changed in the same ways as before.

Last and perhaps most intriguing, the researchers created what they called molecular “signatures” of the levels of a few, representative metabolites that changed with exercise. They then looked for these same patterns of metabolites in stored blood samples gathered decades before from past Framingham participants, while also checking to see if and when any of these volunteers had passed away.

The relevant signatures popped up in some of the blood samples, the researchers found, and these samples tended to be from people who had not died prematurely, suggesting that the kinds of metabolite changes that occur with exercise might influence and improve health well into the future.

That idea is “speculative,” though, says Dr. Gregory Lewis, the section head of the heart failure program and director of the cardiopulmonary exercise laboratory at Massachusetts General Hospital, who oversaw the new study. The decades-old blood samples were drawn during standard medical testing, not after exercise, he says, so some people with desirable metabolite signatures might have been born that way and not needed workouts to remodel their metabolites.

Even among the current volunteers, he points out, different people’s molecules responded somewhat differently to their exercise. Over all, people with obesity developed fewer changes than leaner riders, suggesting they might somehow resist some of the benefits of exercise. Men and women, as groups, also showed slightly discordant molecular signatures, but age did not influence people’s molecular responses.

Larger future ’omics studies should help scientists tease out how and why we each react as we do to exercise, Dr. Lewis says, and enable researchers to define more-precise molecular signatures that might indicate, with a blood test, how fit someone is or how their bodies may respond to different types of exercise.

But for now, the current study underscores just how pervasive and immediate the effects of exercise can be. “This was barely 10 minutes of exercise,” Dr. Lewis says, “but it shifted so much” inside people.

Exercise May Ease Hot Flashes, Provided It’s Vigorous

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Hot flashes are a lamentable part of reaching middle age for many women. While drug treatments may provide relief, two new studies suggest that the right type of exercise might lessen both the frequency and discomfiting severity of hot flashes by changing how the body regulates its internal temperature.

As estrogen levels drop with the onset of menopause, many women become less adept, physiologically, at dealing with changes to internal and external temperatures. The result, famously, is the hot flash (also known as a hot flush), during which women can feel sudden, overwhelming heat and experience copious sweating, a problem that in some cases can linger for years.

Hormone replacement therapy can effectively combat hot flashes, and antidepressants may also help, though drug treatments have well-established side effects. Weight loss also may lessen hot flashes, but losing weight after menopause is difficult.

So researchers at Liverpool John Moores University in England and other institutions recently began to consider whether exercise might help.

Endurance exercise, after all, improves the body’s ability to regulate temperature, the scientists knew. Athletes, especially those in strenuous sports like distance running and cycling, start to sweat at a lower body temperature than out-of-shape people. Athletes’ blood vessels also carry more blood to the skin surface to release unwanted heat, even when they aren’t exercising.

If exercise had a similar effect on older, out-of-shape women’s internal thermostats, the scientists speculated, it might also lessen the number or the intensity of their hot flashes.

Previous studies examining exercise as a treatment for hot flashes had shown mixed results, the scientists knew. However, many of those experiments had been short term and involved walking or similarly light exercise, which might be too gentle to cause the physiological changes needed to reduce hot flashes.

So for the two new studies, one of which was published in the Journal of Physiology and the other in Menopause (using the same data to examine different aspects of exercise and hot flashes), the researchers decided to look at the effects of slightly more strenuous workouts.

They first recruited 21 menopausal women who did not currently exercise but did experience hot flashes. According to diaries each woman kept for a week at the start of the study, some women were having 100 or more of them each week.

The scientists also measured each woman’s general health, fitness, blood flow to the brain (which affects heat responses) and, most elaborately, ability to respond to heat stress. For that test, researchers fitted the women with suits that almost completely covered their bodies. The suits contained tubes that could be filled with water. By raising the temperature of the water, the scientists could induce hot flashes — which typically occur if an affected woman’s skin grows hot — and also track her body’s general ability to deal with heat stress.

Fourteen of the women then began an exercise program, while seven, who served as controls, did not. (This was a small pilot study, and the researchers allowed the women to choose whether to exercise or not.)

The sessions, all of them supervised by trainers, at first consisted of 30 minutes of moderate jogging or bicycling three times a week. Gradually, the workouts became longer and more intense, until by the end of four months the women were jogging or pedaling four or five times per week for 45 minutes at a pace that definitely caused them to pant and sweat.

They also, in the last of those 16 weeks, kept another diary of their hot flashes.

Then they returned to the lab to repeat the original tests.

The results showed that the exercisers, unsurprisingly, were considerably more aerobically fit now, while the control group’s fitness was unchanged.

More striking, the women who had exercised showed much better ability to regulate their body heat. When they wore the suit filled with warm water, they began to sweat a little earlier and more heavily than they had before, showing that their bodies could generally dissipate heat better.

But at the same time, during an actual hot flash induced by the hot suit, the exercisers perspired less and showed a lower rise in skin temperature than the control group. Their hot flashes were less intense than those of the women who had not worked out.

Probably best of all from the standpoint of the volunteers who had exercised, they turned out to have experienced far fewer hot flashes near the end of the experiment, according to their diaries, with the average frequency declining by more than 60 percent.

These findings strongly suggest that “improvements in fitness with a regular exercise program will have potential benefits on hot flushes,” said Helen Jones, a professor of exercise science at Liverpool John Moores University, who oversaw the new studies.

Precisely how exercise might change a women’s susceptibility to hot flashes is still not completely clear, although the researchers noted that the women who exercised developed better blood flow to the surface of their skin and to their brains during heat stress. That heightened blood flow most likely aided the operations of portions of the brain that regulate body temperature, Dr. Jones said.

The cautionary subtext of this study, though, is that to be effective against hot flashes, exercise probably needs to be sustained and somewhat strenuous, she said. “A leisurely walk for 30 minutes once a week is not going to have the required impact.”

To Boost Memory: Study, Wait, Then Exercise

Illustration by Renaud Vigourt

Learning requires more than the acquisition of unfamiliar knowledge; that new information or know-how, if it’s to be more than ephemeral, must be consolidated and securely stored in long-term memory.

Mental repetition is one way to do that, of course. But mounting scientific evidence suggests that what we do physically also plays an important role in this process. Sleep, for instance, reinforces memory. And recent experiments show that when mice and rats jog on running wheels after acquiring a new skill, they learn much better than sedentary rodents do. Exercise seems to increase the production of biochemicals in the body and brain related to mental function.

Researchers at the Donders Institute for Brain, Cognition and Behavior at Radboud University in the Netherlands and the University of Edinburgh have begun to explore this connection. For a study published this month in Current Biology, 72 healthy adult men and women spent about 40 minutes undergoing a standard test of visual and spatial learning. They observed pictures on a computer screen and then were asked to remember their locations.

Afterward, the subjects all watched nature documentaries. Two-thirds of them also exercised: Half were first put through interval training on exercise bicycles for 35 minutes immediately after completing the test; the others did the same workout four hours after the test.

Two days later, everyone returned to the lab and repeated the original computerized test while an M.R.I. machine scanned their brain activity.

Those who exercised four hours after the test recognized and recreated the picture locations most accurately. Their brain activity was subtly different, too, showing a more consistent pattern of neural activity. The study’s authors suggest that their brains might have been functioning more efficiently because they had learned the patterns so fully. But why delaying exercise for four hours was more effective than an immediate workout remains mysterious. By contrast, rodents do better in many experiments if they work out right after learning.

Eelco van Dongen, the study’s lead author and a former researcher at Radboud University (he is now a policy officer at the Netherlands Organization for Scientific Research), hopes that future studies will help determine both the optimal time to exercise and the ideal activity to reinforce learning. Workouts that are too strenuous “could be less positive or even detrimental” to acquiring knowledge, Dr. van Dongen says, while gentle exertions — “a short, slow walk,” he adds — might not prompt enough of an increase in the biochemicals needed to influence how the brain learns.

For now, he says, if you are trying to memorize a PowerPoint narrative or teach yourself macroeconomics, it could be beneficial to exercise a few hours after a study session. “Long-term memory is not only influenced by what happens when you learn new things,” he says, “but also by the processes that take place in the hours and days afterward, when new information is stabilized and integrated in your brain.”

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Being Unfit May Be Almost as Bad for You as Smoking

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Being out of shape could be more harmful to health and longevity than most people expect, according to a new, long-term study of middle-aged men. The study finds that poor physical fitness may be second only to smoking as a risk factor for premature death.

It is not news that aerobic capacity can influence lifespan. Many past epidemiological studies have found that people with low physical fitness tend to be at high risk of premature death. Conversely, people with robust aerobic capacity are likely to have long lives.

But most of those studies followed people for about 10 to 20 years, which is a lengthy period of time for science but nowhere near most of our actual lifespans. Some of those studies also enrolled people who already were elderly or infirm, making it difficult to extrapolate the findings to younger, healthier people.

So for the new study, which was published this week in the European Journal of Preventive Cardiology, researchers from the University of Gothenburg in Sweden and other institutions turned to an impressively large and long-term database of information about Swedish men.

The data set, prosaically named the Study of Men Born in 1913, involved exactly that. In 1963, almost 1,000 healthy 50-year-old men in Gothenburg who had been born in 1913 agreed to be studied for the rest of their lives, in order to help scientists better understand lifetime risks for disease, especially heart disease.

The men completed baseline health testing in 1963, including measures of their blood pressure, weight and cholesterol, and whether they exercised and smoked. Four years later, when the volunteers were 54, some underwent more extensive testing, including an exercise stress test designed to precisely determine their maximum aerobic capacity, or VO2 max. Using the results, the scientists developed a mathematical formula that allowed them to estimate the aerobic capacity of the rest of the participants.

Aerobic capacity is an interesting measure for scientists to study, because it is affected by both genetics and lifestyle. Some portion of our VO2 max is innate; we inherit it from our parents. But much of our endurance capacity is determined by our lifestyle. Being sedentary lowers VO2 max, as does being overweight. Exercise raises it.

Among this group of middle-aged men, aerobic capacities ranged from slight to impressively high, and generally reflected the men’s self-reported exercise habits. Men who said that they seldom worked out tended to have a low VO2 max. (Because VO2 max is more objective than self-reports about exercise, the researchers focused on it.)

To determine what impact fitness might have on lifespan, the scientists grouped the men into three categories: those with low, medium or high aerobic capacity at age 54.

Then they followed the men for almost 50 years. During that time, the surviving volunteers completed follow-up health testing about once each decade. The scientists also tracked deaths among the men, based on a national registry.

Then they compared the risk of relatively early death to a variety of health parameters, particularly each man’s VO2 max, blood pressure, cholesterol profile and history of smoking. (They did not include body weight as a separate measure, because it was indirectly reflected by VO2 max.)

Not surprisingly, smoking had the greatest impact on lifespan. It substantially shortened lives.

But low aerobic capacity wasn’t far behind. The men in the group with the lowest VO2 max had a 21 percent higher risk of dying prematurely than those with middling aerobic capacity, and about a 42 percent higher risk of early death than the men who were the most fit.

Poor fitness turned out to be unhealthier even than high blood pressure or poor cholesterol profiles, the researchers found. Highly fit men with elevated blood pressure or relatively unhealthy cholesterol profiles tended to live longer than out-of-shape men with good blood pressure and cholesterol levels.

Of course, this study found links between poor fitness and shortened lifespans. It cannot prove that one caused the other, or explain how VO2 max might affect lifespan. However, the findings raise the possibility, as the scientists speculate, that by strengthening the body, better fitness may lower the risk of a variety of chronic diseases.

This study also involved men — and Swedish men at that. So whether the findings are applicable to other people, particularly women, is uncertain.

But “there is no reason not to think” that the rest of us would also share any beneficial associations between fitness and longevity, said Per Ladenvall, a researcher at the Sahlgrenska Academy at the University of Gothenburg, who led the study. Past studies involving women have found such links, he said.

Encouragingly, if you now are concerned about the state of your particular aerobic capacity, you most likely can increase it just by getting up and moving. “Even small amounts of physical activity,” Dr. Ladenvall said, “may have positive effects on fitness.”

Lifting Lighter Weights Can Be Just as Effective as Heavy Ones

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Upending conventions about how best to strength train, a new study finds that people who lift relatively light weights can build just as much strength and muscle size as those who grunt through sessions using much heftier weights — if they plan their workouts correctly.

Strength training has long been dominated by the idea that to develop a physique like that of Charles Atlas or even Zac Efron, we — and I include women here — must load our barbells or machines with almost as much weight as we can bear.

In traditional weight training programs, in fact, we are told to first find the heaviest amount of weight that we possibly can lift one time. This is our one-repetition maximum weight. We then use this to shape the rest of the program by lifting 80 to 90 percent of that amount eight to 10 times, until our affected arms or legs shake with fatigue.

This approach to weight training is very effective, says Stuart Phillips, a professor of kinesiology at McMaster University in Hamilton, Ontario, who has long studied muscles and exercise. It builds muscle strength and size, possibly, many experts believe, by sparking a surge in the body’s production of testosterone and human growth hormone.

But many people find lifting such heavy weights to be daunting or downright unpleasant, which can discourage them from taking up or continuing with a resistance-training program, Dr. Phillips says.

So in recent years, he and his colleagues have been looking into the effects of a different type of weight training, which employs much lighter weights hefted through as many as 25 repetitions.

Since 2010, his lab has published several studies in which volunteers followed either the traditional regimen using heavy weights or an alternative that employed much slighter weight stacks. In general, the lifters’ results were comparable.

But those studies had been small and featured volunteers who were new to the gym, potentially skewing the outcomes, Dr. Phillips says. Almost everyone who takes up weight training shows significant improvements in strength and muscle size, making it difficult to tease out the impacts of one version of training versus another.

So for the new study, which was funded by the Natural Sciences and Engineering Research Council of Canada and published this month in the Journal of Applied Physiology, he and his colleagues recruited 49 young men who had been weight training for a year or more. (The scientists plan to study women and older people in future studies.)

All completed tests of strength, fitness, hormone levels and muscular health, then were randomly divided into two groups.

One group was assigned to follow the standard regimen, in which weights were set at between 75 and 90 percent of the man’s one-repetition maximum and the volunteer lifted until he could not lift again, usually after about 10 repetitions.

The other volunteers began the lighter routine. Their weights were set at between 30 and 50 percent of each man’s one-repetition maximum, and he lifted them as many as 25 times, until the muscles were exhausted.

All of the volunteers performed three sets of their various lifts four times per week for 12 weeks.

Then they returned to the lab to have muscle strength, size and health reassessed and their hormone levels re-measured.

The results were unequivocal. There were no significant differences between the two groups. All of the men had gained muscle strength and size, and these gains were almost identical, whether they had lifted heavy or light weights.

Interestingly, the scientists found no connection between changes in the men’s hormone levels and their gains in strength and muscle size. All of the men had more testosterone and human growth hormone flowing through their bodies after the workouts. But the degree of those changes in hormone levels did not correlate with their gains in strength.

Instead, the key to getting stronger for these men, Dr. Phillips and his colleagues decided, was to grow tired. The volunteers in both groups had to attain almost total muscular fatigue in order to increase their muscles’ size and strength.

That finding suggests, Dr. Phillips says, that there is something about the cellular mechanisms jump-started in muscle tissue by exhaustion that enables you to develop arms like the first lady’s.

This data does not prove, though, that one approach to lifting weights is necessarily better than the other, Dr. Phillips says.

“But some people will find it much easier or less intimidating” to lift lighter weights, he says, even though they need to complete more repetitions in order to tire their muscles. They also may experience fewer injuries, he says, although that possibility has not yet been tested.

For now, someone hoping to strengthen his or her muscles should choose a weight that feels tolerable and then lift it repeatedly until the effort of the final lift is at least an eight on a scale of one to 10, Dr. Phillips says. “There should be some discomfort,” he says, “but the dividends on the back side” in terms of stronger, healthier muscles “are enormous.”

Can Running Make You Smarter?

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To strengthen your mind, you may first want to exert your leg muscles, according to a sophisticated new experiment involving people, mice and monkeys. The study’s results suggest that long-term endurance exercise such as running can alter muscles in ways that then jump-start changes in the brain, helping to fortify learning and memory.

I often have written about the benefits of exercise for the brain and, in particular, how, when lab rodents or other animals exercise, they create extra neurons in their brains, a process known as neurogenesis. These new cells then cluster in portions of the brain critical for thinking and recollection.

Even more telling, other experiments have found that animals living in cages enlivened with colored toys, flavored varieties of water and other enrichments wind up showing greater neurogenesis than animals in drab, standard cages. But animals given access to running wheels, even if they don’t also have all of the toys and other party-cage extras, develop the most new brain cells of all.

These experiments strongly suggest that while mental stimulation is important for brain health, physical stimulation is even more potent.

But so far scientists have not teased out precisely how physical movement remakes the brain, although all agree that the process is bogglingly complex.

Fascinated by that complexity, researchers at the National Institutes of Health recently began to wonder whether some of the necessary steps might be taking place far from the brain itself, and specifically, in the muscles, which are the body part most affected by exercise. Working muscles contract, burn fuel and pump out a wide variety of proteins and other substances.

The N.I.H. researchers suspected that some of those substances migrated from the muscles into the bloodstream and then to the brain, where they most likely contributed to brain health.

But which substances were involved was largely a mystery.

So for the new study, which was published last month in Cell Metabolism, the N.I.H. researchers first isolated muscle cells from mice in petri dishes and doused them with a peptide that affects cell metabolism in ways that mimic aerobic exercise. In effect, they made the cells think that they were running.

Then, using a technique called mass spectrometry, the scientists analyzed the many chemicals that the muscle cells released after their pseudo-workouts, focusing on those few that can cross the blood-brain barrier.

They zeroed in on one substance in particular, a protein called cathepsin B. The protein is known to help sore muscles recover, in part by helping to clear away cellular debris, but it had not previously been considered part of the chain linking exercise to brain health.

To determine whether cathepsin B might, in fact, be involved in brain health, the researchers added a little of the protein to living neurons in other petri dishes. They found that those brain cells started making more proteins related to neurogenesis.

Cathepsin B also proved to be abundant in the bloodstreams of mice, monkeys and people who took up running, the scientists found. In experiments undertaken in collaboration with colleagues in Germany, the researchers had mice run for several weeks, while rhesus monkeys and young men and women took to treadmills for four months, exercising vigorously about three times a week for approximately an hour or sometimes longer.

During that time, the concentrations of cathepsin B in the jogging animals and people steadily rose, the researchers found, and all of the runners began to perform better on various tests of memory and thinking.

Most striking, in the human volunteers, the men and women whose fitness had increased the most — suggesting that they had run particularly intensely — not only had the highest levels of cathepsin B in their blood but also the most-improved test scores.

Finally, because there’s nothing like removing something from the body to underscore how important it may be, the scientists bred mice without the ability to create cathepsin B, including after exercise. The researchers had those mice and other, normal animals run for a week, then taxed their ability to learn and retain information.

After running, the normal mice learned more rapidly than they had before and also held on to those new memories well. But the animals that could not produce cathepsin B learned haltingly and soon forgot their new skills. Running had not helped them to become smarter.

The lesson of these experiments is that our brains appear to function better when they are awash in cathepsin B and we make more cathepsin B when we exercise, says Henriette van Praag, an investigator at the National Institute on Aging at the N.I.H. who oversaw this study.

Of course, increases in cathepsin B explain only part of the benefits of exercise for the brain, she said. She and her colleagues plan to continue looking for other mechanisms in future studies.

They also hope to learn more about how much exercise is necessary to gain brain benefits. The regimen that the human runners followed in this study was “fairly intensive,” she said, but it’s possible that lighter workouts would be almost as effective.

“There is good reason to think,” she said, “that any amount of exercise is going to be better than none” for brain health.

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Ask Well: Exercising on ‘Smog Alert’ Days

Smog hangs over New York City in 1966.

Smog hangs over New York City in 1966. Neal Boenzi/The New York Times

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The Surprising Health Benefits of an Electric Bike

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In the Tour de France, equipping your bike with a small electric motor is called mechanical doping, and is considered cheating. But for the rest of us, an electrified bicycle might be a way to make exercise both tolerable and practical, according to an encouraging new study of bicycle commuting.

Exercise is necessary in our lives, as we all know by now. People who are physically active are much less likely than sedentary people to develop heart disease, diabetes, cancer, stroke, depression, disabilities in old age, or to die prematurely.

But statistics show that, despite its benefits, a majority of us never exercise. When researchers ask why, most people offer the same two excuses — they don’t have time to fit exercise into their lives or they aren’t fit enough to undertake exercise.

Potentially, electric bicycles could address those concerns. Their motors shore up your pedaling as needed—or, with some electric bikes, do the pedaling for you—making climbing hills or riding for long distances less taxing and daunting than the same ride on a standard bicycle.

In the process, they could make cycling a palatable alternative to commuting by car, allowing people with jammed daily schedules to work out while getting to work.

But the value of electric bicycles has so far been mostly notional. Few of us have seen, let alone ridden, an electric bike and there is scant scientific evidence supporting—or refuting—the potential health benefits of using the machines.

So for the new experiment, which was published last month in the European Journal of Applied Physiology, researchers at the University of Colorado, Boulder, decided to see what would happen if they gave a group of out-of-shape men and women zippy electric bikes and suggested that they begin riding to work.

Notably, the researchers only studied motorized bikes that assist the rider rather than doing all the work for them, like a moped. They used electric bikes that require the rider to pedal in order to receive assistance from the motor.

The researchers wanted to determine whether these bikes — even with the added assistance of a motor — would provide a meaningful workout for people who previously had not been exercising much. They also wanted to see whether such bikes were fundamentally safe, given that they enable even novice riders to achieve speeds of 20 miles per hour or higher. (The Boulder city government partially funded the study as part of an assessment of whether to allow electric bikes on municipal bike paths. Additional funding came from local bike shops and Skratch Labs, a sports nutrition company in Boulder.)

The researchers first brought their 20 sedentary volunteers into the lab to check their body composition, aerobic fitness, blood sugar control, blood pressure and cholesterol profiles. Then they provided each with an electric bicycle, heart rate monitor, GPS device, instructions on the use of all of this equipment, and asked each volunteer to don the monitors and ride his or her new bike to and from work at least three times a week for the next month, spending at least 40 minutes in the saddle on those days.

The volunteers were directed to choose whatever speed and effort felt comfortable for them.

Then the researchers loosed the novice riders onto Boulder’s roads and bike paths.

A month later, the volunteers returned to the lab to repeat the original tests and turn over heart rate and GPS data. All of them had ridden at least the prescribed minimum of 40 minutes three times per week and in fact, according to their monitor data, most had ridden more than required, several about 50 percent more.

The riders also had ridden with some intensity. Their heart rates averaged about 75 percent of each person’s maximum, meaning that even with the motor assist, they were getting a moderate workout, comparable to brisk walking or an easy jog.

But thankfully none had crashed and hurt themselves (or anyone else). In fact, “we found that participants rode at a reasonable average speed of about 12 miles per hour,” said James Peterman, a graduate student at U.C. Boulder who led the study.

Perhaps most important, the riders were healthier and more fit now, with significantly greater aerobic fitness, better blood sugar control, and, as a group, a trend toward less body fat.

They also reported finding the riding to “be a blast,” said William Byrnes, the study’s senior author and director of the university’s Applied Exercise Science Laboratory. “It’s exercise that is fun.”

Several participants have bought electric bikes since the study ended, he said. He also rides an electric bike to and from campus.

Electric bikes are unlikely to be a solution for everyone who is pressed for time or reluctant to exercise, though. The bikes are pricey, typically retailing for thousands of dollars.

They also offer less of a workout than non-motorized bicycles. Mr. Peterman, an accomplished bike racer who placed fifth in the time trial at the United States National Cycling Championships last week admits that motorized bicycles are unlikely to goose the fitness of well-trained athletes.

But for the many other people who currently do not exercise or have never considered bike commuting, there is much to be said for knowing that, if needed, you can get a little help pedaling up that next hill.

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The Urgency in Fighting Childhood Obesity

Paul Rogers

Life-threatening ailments like heart disease, cancer, stroke and Type 2 diabetes most often afflict adults. But they are often consequences of childhood obesity.

Two new studies, conducted among more than half a million children in Denmark who were followed for many years, linked a high body mass index in children to an increased risk of developing colon cancer and suffering an early stroke as adults. The studies, presented at the European Obesity Summit in Gothenburg, Sweden, this spring, underscore the importance of preventing and reversing undue weight gain in young children and teenagers.

One study, of more than 257,623 people, by Dr. Britt Wang Jensen and colleagues at the Institute of Preventive Medicine, in Bispebjerg, Denmark, and Frederiksberg Hospital in Copenhagen, grouped children according to standard deviations from a mean B.M.I., adjusted for a child’s age and sex.

They found that each unit of increase in being overweight at age 13, generally corresponding to a two- to three-point increase in B.M.I., increased the risk of developing colon cancer by 9 percent and rectal cancer by 11 percent.

The second study, involving 307,677 Danish people born from 1930 to 1987, used a similar grouping of B.M.I. The risk of developing a clot-related stroke in early adult life increased by 26 percent in women and 21 percent in men for each unit of increase in being overweight at all stages of childhood, but especially at age 13.

Although neither study proves that excess weight in childhood itself, as opposed to being overweight as an adult, is responsible for the higher rates of cancer and stroke, overweight children are much more likely to become overweight adults — unless they adopt and maintain healthier patterns of eating and exercise.

According to the American Academy of Child and Adolescent Psychiatry, obesity most often develops from ages 5 to 6 or during the teen years, and “studies have shown that a child who is obese between the ages of 10 and 13 has an 80 percent chance of becoming an obese adult.”

In a study published in 2014 in The New England Journal of Medicine, Solveig A. Cunningham and colleagues at Emory University found that “overweight 5-year-olds were four times as likely as normal-weight children to become obese by age 14.” The study, which involved a representative sample of 7,738 kindergartners, found that the risk of becoming obese did not differ by socioeconomic status, race or ethnic group, or birth weight. Rather, it showed that excess weight gain early in life is a risk factor for obesity later in childhood across the entire population.

Children are generally considered obese when their B.M.I. is at or above the 95th percentile for others of the same age and sex. Currently, about one-third of American children are overweight or obese. By 2012, the Centers for Disease Control and Prevention reports, 18 percent of children and 21 percent of adolescents were obese.

The adverse effects of excess weight in childhood and adolescence don’t necessarily wait to show up later in life. In a review of complications resulting from youthful obesity, Dr. Stephen R. Daniels, a pediatrician at the University of Colorado School of Medicine and the Children’s Hospital in Denver, found that problems in many organ systems were often apparent long before adulthood. They include high blood pressure; insulin resistance and Type 2 diabetes; high blood levels of heart-damaging triglycerides and low levels of protective high-density lipoprotein (HDL) cholesterol; nonalcoholic fatty liver disease; obstructive sleep apnea; asthma; and excess stress on the musculoskeletal system resulting in abnormal bone development, knee and hip pain, and difficulty walking.

Problems of youthful obesity go beyond physical ones. Obese adolescents have higher rates of depression, which in itself may foster poor eating and exercise patterns that add to their weight problem and result in a poor quality of life that persists into adulthood.

In a study conducted in Singapore, researchers reported that “individuals who were obese in childhood are more likely to have poor body image and low self-esteem and confidence, even more so than those with adult onset obesity.”

Another study by Dr. Jeffrey B. Schwimmer of the University of California, San Diego, and colleagues found that obese children and adolescents reported a diminished quality of life that was comparable to that of children with cancer.

Taken together, the data speak to the critical importance of preventing undue weight gain in young children, a task that depends largely on parents, who are responsible for what and how much children eat and how much physical activity they engage in. As researchers from the University Medical Center Groningen in the Netherlands put it, “Early recognition of overweight or obesity in children by their parents is of utmost importance, allowing interventions to start at a young age.” Yet, they found in a study of the parents of 2,203 5-year-olds, “parents underestimated their overweight child in 85 percent of the cases.”

Though it seems logical that parents who think their children are overweight would make a special effort to assure they would “grow into” their weight as they get older, research has shown the opposite. Such children tend to get even fatter, according to findings from the Longitudinal Study of Australian Children reported in April in the journal Pediatrics by Eric Robinson of the University of Liverpool and Angelina R. Sutin of Florida State University College of Medicine.

Even being labeled overweight can itself be damaging and make it harder for children to avoid bad habits, the authors suggested. A 2014 study of girls aged 10 to 19 found that “regardless of actual weight, adolescents who reported having been labeled ‘too fat’ by a family member or peer were more likely to become obese nearly a decade later.”

“I encourage parents to change the environment at home,” Dr. Daniels of the University of Colorado said in an interview. “Without being authoritarian, they should limit high-calorie-dense foods, keep sugar-sweetened beverages out of the house and assure that kids eat the right amount of fruits and vegetables and fewer calorie-dense snacks. Parents also need to be tuned into opportunities for physical activity and set hard-and-fast rules about television and time spent on electronics.”

Following the “5210” daily program endorsed by the American Academy of Pediatrics can help: Aim for five fruits and vegetables a day; keep recreational screen time to two hours or less; include at least one hour of active play: and skip sugar-sweetened beverages and drink water.

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Could Environmental Chemicals Shape Our Exercise Habits?

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A disquieting new study finds that mice exposed prenatally to a common chemical found in many cosmetics and personal care products are less likely than other mice to exercise as adults, adding a new wrinkle to the mystery of exercise motivation. Although mice obviously are not people, the findings at least raise the possibility that exposure to environmental toxins before birth might change babies’ physiology in ways that affect their interest in exercise throughout their lives.

By now, we all know that we should work out to improve health and well-being. But a hefty majority of us never manage to exercise and many who do visit the gym do so reluctantly and sporadically.

The question of why some people are so loath to exercise is of pressing interest to exercise scientists. Work and family obligations of course play an outsize role, as do genes. Studies of the genetics of exercise suggest in fact that the will to exercise — or not — is mostly inherited.

But scientists also have begun to wonder about early physical development and whether differences in the environment within a mother’s womb might lead to changes in her baby that affect how much that infant moves around later in life.

A mouse study I wrote about recently suggested, encouragingly, that if a mother exercises during pregnancy, she might increase her offspring’s subsequent interest in working out.

But whether the environment within the womb might reduce a baby’s later desire to exercise has not been much studied.

So for the new study, which will appear next month in Medicine & Science in Sports & Exercise, scientists at Texas A&M University in College Station, Tex., decided to look at pregnancy, exercise behavior and phthalates.

Phthalates (THAL-ates) are a class of chemicals used as solvents and fixatives and to make plastic pliable. Found today in a boggling array of everyday products, from food containers to shampoos and perfume, they are virtually ubiquitous in the environment and in our bloodstreams.

They easily cross into a pregnant woman’s womb and accumulate in her offspring. Rather ominously, phthalates are known as endocrine disrupters, meaning that they can change the body’s production of the sex hormones testosterone and estrogen and, in animal studies, alter the onset of puberty in mouse pups exposed to high levels of the chemicals in utero.

The Texas scientists wondered whether phthalates might also influence how much exposed babies exercised, since varying levels of sex hormones, especially testosterone, are known to change how readily young animals move around.

To find out, they gathered healthy female mice, mated them with healthy males, and then fed half of the pregnant females benzyl butyl phthalate (B.B.P.), a common phthalate. The mice received the B.B.P. at the point in their pregnancies when their babies were rapidly developing organs and sex characteristics, which in human terms, would be near the end of the second trimester.

According to the scientists’ calculations, the exposure for each pup would be slightly higher than the amount that the E.P.A. has determined to be safe for humans.

The rest of the pregnant animals were fed a harmless oil to serve as a control group.

After birth, all of the pups were provided with running wheels and allowed to exercise as much or little as they chose.

The scientists checked the animals’ sex hormone levels at several points during the animals’ lives.

What the researchers found was that by young adulthood and continuing on into the mouse version of late middle age, the exposed animals were not moving much.

In fact, the male mice that had been exposed to B.B.P. in utero ran about 20 percent less during adulthood than the other animals, while the exposed females exercised about 15 percent less.

Interestingly, the exposed animals did not differ much from the other rodents in terms of body composition. They were not significantly fatter. Obesity and any accompanying disability had not discouraged them from exercising, the scientists concluded. They had been sedentary by choice, not necessity.

That choice, however, seems to have been influenced by disruptions in their sex hormones. Checking their data, the researchers found that the male mice exposed to B.B.P. in utero had notably lower levels of testosterone than the other animals in young adulthood, which is also when their running mileage cratered. Those differences lingered into middle age. The exposed females similarly developed during young adulthood low estrogen levels and other reproductive system abnormalities that then produced a profound desire, it seems, to sit for most of the day.

The implication of these findings is that, in mice, “exposure to the endocrine disrupter B.B.P. might affect lifelong physical activity,” said Emily Schmitt, a postdoctoral researcher at Texas A&M who led the new study.

It’s impossible at this point to say whether human babies would be similarly affected, Dr. Schmitt said.

Likewise scientists don’t know whether a father’s exposure to phthalates can affect his unborn offspring or if eating and dousing oneself in phthalates long after birth, including when you are fully grown, might dampen your subsequent enthusiasm for working out, although Dr. Schmitt and her colleagues hope to investigate some of those issues in future studies.

But even with many questions remaining unanswered, “it certainly seems like a good idea to try to avoid endocrine disruptors as much as possible, especially if you are pregnant,” Dr. Schmitt said.

You can find tips for reducing exposure to the chemicals at saferchemicals.org/.

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How Many Calories We Burn When We Sit, Stand or Walk

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There are many compelling reasons to get up out of your desk chair and stand more at work. But weight control is probably not one of them, according to a new study that precisely measured how many calories people burn during everyday office activities.

The new study’s results suggest that engaging frequently in one type of activity while at work may help many of us avoid weight gain. But that activity is not standing up.

Most of us sit more than we should, and a majority of our sitting time occurs at work, since many modern professions are sedentary. Many of us spend six or seven hours tied to our desks each day.

These long, uninterrupted periods of physical lethargy have been linked with increased risks for diabetes, heart disease, premature mortality and, not least, weight gain.

In response, many people, including me, have begun to look for ways to break up our sitting time. We download smartphone apps that chirp and tell us to stand up several times every hour. Health-minded supervisors organize walking meetings, in which employees discuss business while hoofing along hallways. And standing desks have become so popular that the satirical website The Onion has poked fun at users, declaring “Standing at Work Can Increase Coworkers’ Disdain Up to 70 Percent.”

Recent studies indicate that measures that get us off our seats can help us better regulate blood sugar and lessen the risks for diabetes and chronic disease. But more to the point, many of us are rising from our chairs in the hopes that sitting less will help keep our waistlines and nether quarters from spreading.

Surprisingly few studies, however, have closely tracked how many additional calories we burn if we stand up or walk around our offices.

So for the new experiment, which was published this month in the Journal of Physical Activity and Health, researchers affiliated with the Physical Activity and Weight Management Research Center at the University of Pittsburgh rounded up 74 healthy volunteers. Most were in their mid-20s, of normal weight, and with some acquaintance with office life.

These volunteers were randomly assigned to four different groups. One group was asked to sit and type at a computer for 15 minutes and then stand up for 15 minutes, moving around and fidgeting as little as possible.

Another group also sat for 15 minutes, but watched a television screen and didn’t type. Afterward, they immediately moved to a treadmill and walked for 15 minutes at a gentle, strolling pace.

The third group stood up for 15 minutes and then sat down for 15 minutes.

And the final group walked on the treadmills for 15 minutes and then sat.

Throughout, the volunteers wore masks that precisely measured their energy expenditure, which means how many calories they were using.

Unsurprisingly, sitting was not very taxing. The volunteers generally burned about 20 calories during their 15 minutes of sitting, whether they were typing or staring at a television screen.

More unexpected, standing up was barely more demanding. While standing for 15 minutes, the volunteers burned about 2 additional calories compared to when they sat down. It didn’t matter whether they stood up and then sat down or sat down and then stood up. The total caloric expenditure was about the same and was not sizable.

Over all, in fact, the researchers concluded, someone who stood up while working instead of sitting would burn about 8 or 9 extra calories per hour. (Just for comparison, a single cup of coffee with cream and sugar contains around 50 calories.)

But walking was a different matter. When the volunteers walked for 15 minutes, even at a fairly easy pace, they burned about three times as many calories as when they sat or stood. If they walked for an hour, the researchers calculated, they would incinerate about 130 more calories than if they stayed in their chairs or stood up at their desks, an added energy expenditure that might be sufficient, they write, to help people avoid creeping, yearly weight gain.

The upshot of this experiment is that if your goal is to control your weight at work, then “standing up may not be enough,” said Seth Creasy, a graduate student at the University of Pittsburgh and the lead author of the new study.

You probably need to also incorporate walking into your office routine, he said. Maybe “put the printer at the other end of the hallway, or get up to walk to the water fountain every hour or so” instead of keeping a water bottle at your desk.

“Brief periods of walking can add up to make a big difference” in energy expenditure, he said, while standing barely budges your caloric burn.

Of course, standing up almost certainly has other health benefits apart from weight management, Mr. Creasy said, including better blood sugar control and less back and shoulder pain associated with hunching in a chair all day. So don’t dismantle or abandon your stand-up desk just yet. But don’t expect it to counteract that extra cookie with lunch.

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Talking to Younger Men About Growing Old

For Robert Goldfarb, 85, resisting the decline of old age goes beyond the treadmill.

For Robert Goldfarb, 85, resisting the decline of old age goes beyond the treadmill.

An electronic display on the treadmill in my local gym reminds me I’m not only running on the machine, but out of time. Its graph comparing changes in the runner’s heart rate to that of peers goes no further than age 70. I’m 85, and find it ominous that the machine presumes that anyone that old shouldn’t be on the thing.

Reminders that I’m now officially one of the old-old appear with greater frequency. Some are subtle, like the treadmill display; others are more jarring, like my daughter’s approaching 60th birthday. Most reminders are well-meaning: a young woman offering her seat on a bus, an airport employee hurrying over with a wheelchair, happily telling me I won’t have to walk to the gate or stand in line. I graciously decline their kindness, struggling not to protest, “But, I’m a competitive runner!” That I feel robust doesn’t matter; the man I see and the man they see are two very different people.

I recently read something the philosopher Montaigne wrote over 400 years ago: “The shorter my possession of life, the deeper and fuller I must make it.” His words inspired me to seek a path through old age without surrendering to it or ignoring its reality.

I began by fighting memory lapses. Rather than substituting “whatever” for an elusive word, I now strain to recall that word, even if means asking others to bear with me for a bit. I avoid phrases that suggest the end of things, like “downsizing” or “I no longer do that.” I subscribe to internet memory games. To recapture the excitement I felt in long-ago classrooms, I began rereading books I read in college.

I also decided to reach out to men my age to learn how they navigate through growing old. Like most of the men I began speaking with, I’m a product of the 1950s and its pressure to conform, to avoid risk, to shun anything that marked one as “different.” Many young people then were warned by parents that signing petitions bearing words like “protest” or “progressive” would get them rejected for a job or fired when they grew up. Men in my platoon didn’t embrace when we parted after serving in the Korean War. Closer than brothers, we settled for a handshake, knowing that’s what men did.

Almost immediately, I found conversations with men my age awkward. Attempts I made to discuss aging were met with jokes about the alternative. With few exceptions, those I spoke with regarded feelings as something to be endured, not discussed. It quickly became clear I was free to contemplate growing old, but not with them.

My wife suggested I meet with younger acquaintances to learn if they would talk with me about aging. I did, and found that men just 10 years younger spoke openly about changes in their minds and bodies. No one joked or changed the subject when one of them confided, “My father had Alzheimer’s, and I’m beginning to forget the same things he did,” or, “My firm’s managing partner said I was slowing younger associates and had to retire.”

It puzzled me that they felt so much freer to discuss feelings than men born just a decade earlier. Could it be because they were shaped by the ’60s, rather than the ’50s? Growing up, they protested what we accepted, challenged authority we obeyed, celebrated their individuality while we hoped to be one of the men in a gray flannel suit. They were the “me” generation, defined by Woodstock and rock ‘n’ roll, while my generation found comfort in Eisenhower’s paternal leadership and listening to soothing ballads like George Shearing’s “I’ll Remember April” and Margaret Whiting’s “Moonlight in Vermont.” Separated by a sliver of time, the two decades seem an eternity apart.

As I seek to reinvent myself, questioning what I do out of habit and what I’m not doing that could be liberating, it’s the voices of these younger men that I hear as I run on the treadmill today. That and the voice of Frank Sinatra from the ’50s, crooning a line from “September Song” that captures what I’ve been feeling: “But the days grow short when you reach September.” It’s realizing that I’ve reached November that presses me forward, ignoring the treadmill’s display, hoping I can lead a deeper and fuller life before I run out of time.

Robert W. Goldfarb is a management consultant and author of “What’s Stopping Me From Getting Ahead?”

How Exercise May Help the Brain Grow Stronger

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Physical activity is good for our brains. A wealth of science supports that idea. But precisely how exercise alters and improves the brain remains somewhat mysterious.

A new study with mice fills in one piece of that puzzle. It shows that, in rodents at least, strenuous exercise seems to beneficially change how certain genes work inside the brain. Though the study was in mice, and not people, there are encouraging hints that similar things may be going on inside our own skulls.

For years, scientists have known that the brains of animals and people who regularly exercise are different than the brains of those who are sedentary. Experiments in animals show that, for instance, exercise induces the creation of many new cells in the hippocampus, which is a part of the brain essential for memory and learning, and also improves the survival of those fragile, newborn neurons.

Researchers believe that exercise performs these feats at least in part by goosing the body’s production of a substance called brain-derived neurotropic factor, or B.D.N.F., which is a protein that scientists sometimes refer to as “Miracle-Gro” for the brain. B.D.N.F. helps neurons to grow and remain vigorous and also strengthens the synapses that connect neurons, allowing the brain to function better. Low levels of B.D.N.F. have been associated with cognitive decline in both people and animals. Exercise increases levels of B.D.N.F. in brain tissue.

But scientists have not understood just what it is about exercise that prompts the brain to start pumping out additional B.D.N.F.

So for the new study, which was published this month in the journal eLIFE, researchers with New York University’s Langone Medical Center and other institutions decided to microscopically examine and reverse engineer the steps that lead to a surge in B.D.N.F. after exercise.

They began by gathering healthy mice. Half of the animals were put into cages that contained running wheels. The others were housed without wheels. For a month, all of the animals were allowed to get on with their lives. Those living with wheels ran often, generally covering several miles a day, since mice like to run. The others remained sedentary.

After four weeks, the scientists looked at brain tissue from the hippocampus of both groups of animals, checking for B.D.N.F. levels. As expected, the levels were much higher in the brains of the runners.

But then, to better understand why the runners had more B.D.N.F., the researchers turned to the particular gene in the animals’ DNA that is known to create B.D.N.F. For some reason, the scientists realized, this gene was more active among the animals that exercised than those that did not.

Using sophisticated testing methods, the scientists soon learned why. In both groups of animals, the B.D.N.F. gene was partially covered with clusters of a particular type of molecule that binds to the gene, though in different amounts.

In the sedentary mice, these molecules swarmed so densely over the gene that they blocked signals that tell the gene to turn on. As a result, the B.D.N.F. genes of the sedentary animals were relatively muted, pumping out little B.D.N.F.

But among the runners, the molecular blockade was much less effective. The molecules couldn’t seem to cover and bind to the entire B.D.N.F. gene. So messages from the body continued to reach the gene and tell it to turn on and produce more B.D.N.F.

Perhaps most remarkably, the researchers also found a particular substance in the runners’ brains that fended off the action of these obstructionist molecules. The runners’ brains contained high levels of ketones, which are a byproduct of the breakdown of fat. During strenuous exercise, the body relies in part on fat for fuel and winds up creating ketones, some of which migrate to the brain. (They are tiny enough to cross the blood-brain barrier.) The brain uses these ketones for fuel when blood sugar levels grow low.

But it appears that ketones also cause the molecules that hinder the B.D.N.F. gene to loosen their grip, as the scientists realized when they experimentally added ketones to brain tissue from some of the mice. Afterward, their B.D.N.F. genes were not blocked by nearly as many of the bothersome molecules, and those genes could get on with the job of making B.D.N.F.

None of this occurred in the brains of the sedentary mice.

“It’s incredible just how pervasive and complex the effects of exercise are on the brain,” said Moses Chao, a professor at the Skirball Institute of Biomolecular Medicine at N.Y.U. who oversaw the study.

Whether the same mechanisms that occur in mice occur in our own brains when we exercise is still unknown. But, Dr. Chao pointed out, like the mice, we have more B.D.N.F. in our bodies after exercise. We also create ketones when we exercise, and those ketones are known to migrate to our brains..

Generally, however, this process requires exerting yourself vigorously for an hour or more, after which time your body, having exhausted its stores of sugar, starts burning stored fat and making ketones.

If an hour or more of intense exercise seems daunting — and it does to me — don’t despair. “We are only starting to understand” the many ways in which exercise of any kind and amount is likely to alter our brains, Dr. Chao said. For now, he says, “it’s a very good idea to just keep moving.”

Yoga May Be Good for the Brain

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A weekly routine of yoga and meditation may strengthen thinking skills and help to stave off aging-related mental decline, according to a new study of older adults with early signs of memory problems.

Most of us past the age of 40 are aware that our minds and, in particular, memories begin to sputter as the years pass. Familiar names and words no longer spring readily to mind, and car keys acquire the power to teleport into jacket pockets where we could not possibly have left them.

Some weakening in mental function appears to be inevitable as we age. But emerging science suggests that we might be able to slow and mitigate the decline by how we live and, in particular, whether and how we move our bodies. Past studies have found that people who run, weight train, dance, practice tai chi, or regularly garden have a lower risk of developing dementia than people who are not physically active at all.

There also is growing evidence that combining physical activity with meditation might intensify the benefits of both pursuits. In an interesting study that I wrote about recently, for example, people with depression who meditated before they went for a run showed greater improvements in their mood than people who did either of those activities alone.

But many people do not have the physical capacity or taste for running or other similarly vigorous activities.

So for the new study, which was published in April in the Journal of Alzheimer’s Disease, researchers at the University of California, Los Angeles, and other institutions decided to test whether yoga, a relatively mild, meditative activity, could alter people’s brains and fortify their ability to think.

They began by recruiting 29 middle-aged and older adults from the Los Angeles area who told the researchers that they were anxious about the state of their memories and who, during evaluations at the university, were found to have mild cognitive impairment, a mental condition that can be a precursor to eventual dementia.

The volunteers also underwent a sophisticated type of brain scan that tracks how different parts of the brain communicate with one another.

The volunteers then were divided into two groups. One began a well-established brain-training program that involves an hour a week of classroom time and a series of mental exercises designed to bolster their memory that volunteers were asked to practice at home for about 15 minutes a day.

The others took up yoga. For an hour each week, they visited the U.C.L.A. campus to learn Kundalini yoga, which involves breathing exercises and meditation as well as movement and poses. The researchers chose this form of yoga largely because people who are out of shape or new to yoga generally find it easy to complete the classes.

The yoga group also was taught a type of meditation known as Kirtan Kriya that involves repeating a series of sounds — a mantra — while simultaneously “dancing” with repetitive hand movements. They were asked to meditate in this way for 15 minutes every day, so that the total time commitment was equivalent for both groups.

The volunteers practiced their programs for 12 weeks.

Then they returned to the university’s lab for another round of cognitive tests and a second brain scan.

By this time, all of the men and women were able to perform significantly better on most tests of their thinking.

But only those who had practiced yoga and meditation showed improvements in their moods — they scored lower on an assessment of potential depression than those in the brain-training group — and they performed much better on a test of visuospatial memory, a type of remembering that is important for balance, depth perception and the ability to recognize objects and navigate the world.

The brain scans in both groups displayed more communication now between parts of their brains involved in memory and language skills. Those who had practiced yoga, however, also had developed more communication between parts of the brain that control attention, suggesting a greater ability now to focus and multitask.

In effect, yoga and meditation had equaled and then topped the benefits of 12 weeks of brain training.

“We were a bit surprised by the magnitude” of the brain effects, said Dr. Helen Lavretsky, a professor of psychiatry at U.C.L.A. who oversaw the study.

How, physiologically, yoga and meditation had uniquely changed the volunteers’ brains is impossible to know from this study, although reductions in stress hormones and anxiety are likely to play a substantial role, she said. “These were all people worried about the state of their minds,” she pointed out.

Movement also increases the levels of various biochemicals in the muscles and brains that are associated with improved brain health, she said.

Whether other forms of yoga and meditation or either activity on its own might likewise bulk up the brain remains a mystery, she said. But there may be something especially potent, she said, about combining yoga with the type of meditation practiced in this study, during which people were not completely still.

The Alzheimer’s Research and Prevention Foundation, which partially funded this study, provides information on its website about how to start meditating in this style, if you would like to try.

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Exercise Tied to Lower Risk for 13 Types of Cancer

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Anyone who still needs motivation to move more may find it in a new study showing that, in addition to its other health benefits, exercise appears to substantially reduce the risk of developing 13 different varieties of cancer. That is far more types than scientists previously thought might be impacted by exercise. The comprehensive study also suggests that the potential cancer-fighting benefits of exercise seem to hold true even if someone is overweight.

The idea that exercise might change someone’s susceptibility to cancer is, of course, not new. Many studies have found that people who are physically active, either through exercise or while on the job, tend to be less likely to develop certain types of cancer than people who are sedentary.

But those studies primarily looked at associations between exercise and a few common malignancies, such as breast cancer in women, and colon and lung cancers in both women and men.

Whether physical activity, and more precisely, regular exercise, would also lower our risk for other cancers has remained an open question.

So for the new study, which was published this week in JAMA Internal Medicine, scientists with the division of cancer epidemiology and genetics at the National Cancer Institute, as well as Harvard Medical School, and a number of other institutions around the world turned to a large trove of epidemiological health studies conducted in the United States or Europe.

In these earlier studies, researchers directly measured volunteers’ body mass and other health markers and also asked about their diets and exercise habits. The researchers then tracked the participants for a decade or more, noting disease diagnoses or, in some instances, deaths.

Such studies help to establish links between lifestyles and disease risk. But the number of people involved must be hefty if the associations are to be persuasive.

To gain sufficient numbers now, the Cancer Institute researchers gathered data from 12 large-scale studies that, pooled together, involved 1.44 million men and women.

The researchers focused on specific information for each of those 1.44 million people about whether they exercised, and how vigorously and how often. They also zeroed in on whether and when, after each study’s start, the participant had been diagnosed with any type of cancer.

Then, using elaborate statistical methods, they computed the role that exercise, and in particular, moderate or vigorous exercise such as brisk walking or jogging, seemed to be playing in people’s risks for cancer.

It turned out to be considerable. For most cancers, people who reported exercising moderately, even if the time that they spent exercising was slight, had significantly less risk of developing 13 different types of cancer than people who were sedentary.

The researchers found a reduced risk of breast, lung and colon cancers, which had been reported in earlier research. But they also found a lower risk of tumors in the liver, esophagus, kidney, stomach, endometrium, blood, bone marrow, head and neck, rectum and bladder.

And the reductions in risk for any of these 13 cancers rose steeply as people exercised more. When the researchers compared the top 10 percent of exercisers, meaning those who spent the most time each week engaging in moderate or vigorous workouts, to the 10 percent who were the least active, the exercisers were as much as 20 percent less likely to develop most of the cancers in the study.

On the other hand, they found an increased risk of two types of malignancies — melanoma and slow-growing prostate tumors — among people who exercised the most. Those findings can most likely be explained, in large part, by certain characteristics of active people, said Steven Moore, an investigator at the National Cancer Institute who led the study.

“People who exercise generally go in for more checkups” than sedentary people, he said, resulting in more screenings for conditions such as so-called indolent prostate cancers. (There was no discernible association, positive or negative, between exercise and aggressive prostate tumors.) “They also often exercise outside,” he continued, “and are more prone to sunburns” than people who rarely work out, potentially contributing to a greater risk for melanoma.

Encouragingly, the associations between exercise and reduced cancer risks held true even when the researchers factored in body mass. People who were overweight or obese but exercised had a much lower risk of developing most cancers than overweight people who did not move much.

Just how physical activity may be undercutting the risk for so many disparate types of cancers is not yet fully understood, Dr. Moore said, although he and his colleagues suspect that changes in exercisers’ hormone levels, degree of inflammation, digestion and overall energy balance most likely contribute.

Bear in mind, though, that this was an observational study, so it cannot directly prove that exercise reduces cancer risks, only that there is an association between more exercise and less disease. It also relied on participants’ memories of exercise, which can be unreliable.

But even with those limitations, the findings sturdily suggest that exercise may help to reduce the risk of many types of cancer, “and it has few side effects and doesn’t cost much,” said Dr. Moore, who runs almost every day.

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Can High-Intensity Exercise Help Me Lose Weight? And Other Questions, Answered

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I recently wrote about a study showing that one minute of intense interval training, tucked into a workout that was, in total, 10 minutes long, produced comparable health and fitness benefits to 45 minutes of more moderate, uninterrupted endurance training.

Readers posted almost 400 comments to the article and flooded the Internet and my inbox with questions and sentiments about extremely short workouts. Given the extent of the response and the astuteness of the questions, I thought I would address some of the issues that arose over and over.

Q. Are high-intensity interval workouts actually better for you than longer, endurance-style workouts — or just shorter?

A. Better is such a subjective word. At the moment, the two types of workouts appear to be largely equivalent to each other in terms of a wide variety of health and fitness benefits.

In the study that I wrote about, “1 Minute of All-Out Exercise May Equal 45 Minutes of Moderate Exertion,” for instance, three months of high-intensity interval training practiced three times per week led to approximately the same improvements in aerobic endurance, insulin resistance and muscular health as far longer sessions of moderate pedaling on a stationary bicycle.

One type of workout was not more beneficial than the other, in other words, but one required much, much less time.

Other studies have generally produced similar results, although, to be honest, the science related to interval training for health purposes and not simply for athletic performance remains scant. An interesting new review of past research to be published in June did conclude that, for overweight and obese children, short sessions of intense intervals may lead to greater improvements in endurance and blood pressure than longer bouts of moderate exercise, although the authors did not discuss how best to get children to complete frequent interval sessions.

The upshot of the available science is that if you currently have the time and inclination to complete long-ish, moderate workouts — if you enjoy running, cycling, swimming, walking or rowing for 30 minutes or more, for instance — by all means, continue.

If, on the other hand, you frequently skip workouts because you feel that you do not have enough time to exercise, then very brief, high-intensity intervals may be ideal for you. They can robustly improve health and fitness without overcrowding schedules.

Q.

What about combining brief high-intensity workouts with longer, endurance workouts?

A.

Alternating high-intensity workouts with endurance-style workouts may yield the greatest health and fitness gains of all.

In a 2014 study, a group of sedentary adults began either a standard endurance-training program, in which they pedaled a bicycle moderately for 30 minutes five times a week, or swapped one of those bike rides for an interval session. All of the participants wound up significantly more aerobically fit after 12 weeks.

But the men and women who had completed one interval session per week had developed slightly more overall endurance than the other volunteers. As a result, they had lowered their risk for premature death by about an additional 18 percent, the study’s authors conclude.

Q.

Do I have to use a stationary bicycle for interval training?

A.

Most recent studies of high-intensity intervals have involved computerized stationary bicycles because scientists can easily monitor the riders’ pace and intensity. But there is nothing magical about the equipment. The key to high-intensity interval training is the intensity, which most of us can gauge either with a heart rate monitor or our own honest judgment.

For moderate exercise, your heart rate typically should be between 70 and 85 percent of your maximum. (I recently wrote about how to determine your individual maximum heart rate.) This intensity would feel like about an 8 on an arduousness scale of 1 to 10.

During an intense interval, however, your heart rate should rise to 90 percent of your maximum heart rate, or above. Think of this as feeling like about a 9.5 on the 10-point scale. You maintain that intensity for only 10 or 20 seconds at a time, however, followed by several minutes of very easy exercise before repeating the intense work.

Almost any type of exercise can be used for interval training, including running up the stairs in your office’s stairwell during your lunch hour, said Martin Gibala, a professor of kinesiology at McMaster University in Hamilton, Ontario, and an expert on intervals. (His book about the science and practical implications of high-intensity interval training will be published in early 2017.)

Q.

Will high-intensity intervals help me to lose weight?

A.

Few studies have yet looked at the long-term effects on body weight of exercising exclusively with high-intensity intervals, although some experiments do hint that high-intensity interval training can reduce body fat, at least in the short term.

In a 2015 study, for example, overweight, out-of-shape men who began either to jog or otherwise exercise moderately for an hour five days per week for six weeks or to complete intensive interval training for a few minutes per week all dropped body fat and about the same percentages of fat, despite very different amounts of exercise. Likewise, a group of women recovering from breast cancer who were assigned either to moderate exercise or brief interval training for three weeks lost comparable amounts of body fat during the study.

But these were small-scale, brief experiments. Whether interval training helps or hinders long-term weight control is still unknown.

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Yoga for the Showoff. Namaste.

Practicing handstands at Pure Yoga. “You will never be more focused than when you are upside down,” said Kiley Holliday, an instructor.

Practicing handstands at Pure Yoga. “You will never be more focused than when you are upside down,” said Kiley Holliday, an instructor. Nicole Bengiveno/The New York Times

Chip Foley has competed in 50 triathlons, but now he’s turning his focus upside down. “My ultimate goal is to be able to do a handstand and hold it for 30 seconds,” he said.

To achieve the feat, he is pursuing a rigorous training regimen: attending daily classes at Lyons Den Power Yoga, a studio in TriBeCa that specializes in hot yoga; studying handstand videos on YouTube; and doing core-strengthening exercises at home four or five times a week. “I’m obsessed with it,” said Mr. Foley, 38, who spends his right-side-up time as the owner of a Manhattan-based technology consulting firm.

Why the fixation? Social media could be the culprit. Sarah Turk, a lead analyst with IBISWorld, a market research firm, said yoga poses lent themselves to showing off. And Instagram has the numbers to support that statement: The hashtag “yogaeverydamnday” has racked up over five million posts; #handstand and #handstands, over 400,000.

“There’s a level of badassness to it,” said Metta Murdaya, 41, who has been working on her handstand for the past two years. Ms. Murdaya, co-founder of JUARA Skincare, said her inversion practice made her feel more confident, fearless and focused, which she channels into her work as an entrepreneur.

“Literally, you succeed because you refuse to fail,” she said.

The rise of the inversion comes with the rise of the yoga and Pilates industry in the United States, which brought in an estimated $9.1 billion in 2015, according to an IBISWorld report prepared by Ms. Turk. A Yoga in America study recently found that the number of yoga students increased to 36 million in 2016 from 20.4 million in 2012.

Owners of trendy studios that have cropped up to meet New Yorkers’ demands for new ways to practice yoga, like Lyons Den, Pure Yoga and Y7 Studio, said that they had noticed an uptick in requests for inversion workshops and time devoted to handstands and headstands in class. Y7, which holds yoga classes set to pop and hip-hop music in rooms heated by infrared light, has already held four sold-out, two-hour inversion workshops this year, said Sarah Larson Levey, a founder of the studio.

“There’s a level of badassness to it,” said Metta Murdaya, 41, who has been working on her handstand for the past two years.

“There’s a level of badassness to it,” said Metta Murdaya, 41, who has been working on her handstand for the past two years. Juara Skincare

Kiley Holliday, who teaches at Pure Yoga and Equinox in Manhattan, says handstands are popular among her students because of the feeling of accomplishment they experience when they are finally able to do them.

Inversions help students be present in the moment, a perennial objective among yogis, she added. “You will never be more focused than when you are upside down,” Ms. Holliday said. “It is impossible to think of anything else than what you are doing.”

The danger, of course, is taking a tumble, which for many is a rite of passage. “We all fall,” said Lauren Abramowitz, 39, founder of Park Avenue Skin Solutions, who has posted pictures of herself online in an advanced-level scorpion pose (a handstand with a backbend). “It’s not a matter of if, it’s how do you get back up.”

Dr. Gregory Galano, an orthopedic surgeon affiliated with Lenox Hill Hospital, said he often saw patients with yoga-related injuries. “Doing repetitive or long-lasting handstands can lead to everything from low-grade wrist sprains and tendinitis to more serious labral tears in the shoulder,” he said.

He recommends that people slowly work up to more challenging poses. “You want to do things in a controlled and safe manner,” Dr. Galano said.

Instagram users show off their poses.

Instagram users show off their poses. From left: Melissa Perlzweig, Lauren Abramowitz and Elina Lin

To that end, the trainer Kira Stokes prepares students for handstands with a variety of core-strengthening moves in her Stoked 360 class at BFX Studio, the studio brand of New York Sports Clubs, owned by Town Sports International. One of her favorite exercises, a pike on a stability ball that involves bringing the hips over the shoulders, also helps improve shoulder stability and balance.

“Its more than a good party trick,” Ms. Stokes said of achieving a handstand. “It takes strength, balance, coordination and body awareness — all in one move.” She likes to do them, she said, because the practice “boosts my energy and is great for the circulatory system.”

For those who are starting out, just propping your legs against a wall and breathing deeply can give you some of the same energy-boosting benefits, said Sally Melanie Lourenco, a yoga and meditation teacher. “A lot of people aren’t comfortable flipping their world upside down.”

EMAIL: fitcity@nytimes.com

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To Keep Obesity at Bay, Exercise May Trump Diet

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Young rats prone to obesity are much less likely to fulfill that unhappy destiny if they run during adolescence than if they do not, according to a provocative new animal study of exercise and weight. They also were metabolically healthier, and had different gut microbes, than rats that keep the weight off by cutting back on food, the study found. The experiment was done in rodents, not people, but it does raise interesting questions about just what role exercise may play in keeping obesity at bay.

For some time, many scientists, dieting gurus and I have been pointing out that exercise by itself tends to be ineffective for weight loss. Study after study has found that if overweight people start working out but do not also reduce their caloric intake, they shed little if any poundage and may gain weight.

The problem, most scientists agree, is that exercise increases appetite, especially in people who are overweight, and also can cause compensatory inactivity, meaning that people move less over all on days when they exercise. Consequently, they wind up burning fewer daily calories, while also eating more. You do the math.

But those discouraging studies involved weight loss. There has been much less examination of whether exercise might help to prevent weight gain in the first place and, if it does, how it compares to calorie restriction for that purpose.

So for the new study, which was published last week in Medicine & Science in Sports & Exercise, researchers at the University of Missouri in Columbia and other schools first gathered rats from a strain that has an inborn tendency to become obese, starting in adolescence. (Adolescence is also when many young people begin to add weight.)

These rats were young enough, though, that they were not yet overweight.

After weighing them, the researchers divided the animals into three groups.

One group was allowed to eat as much kibble as they wished and to remain sedentary in their cages. These were the controls.

Another group, the exercise group, also was able to eat at will, but these animals were provided with running wheels in their cages. Rats like to run, and the animals willingly hopped on the wheels, exercising every day.

The final group, the dieting group, was put on a calorie-restricted meal plan. Their daily kibble helpings were about 20 percent smaller than the amount that the runners ate, a portion size designed to keep them at about the same weight as the runners, so that extreme differences in body size would not affect the final results.

After 11 weeks, all of the animals were moved to specialized cages that could measure their metabolisms and how much they moved around. They then returned to their assigned cages for several more weeks, by which time they were effectively middle-aged.

At that point, the control animals were obese, their physiques larded with fat.

The runners and the lower-calorie groups, however, although they also had gained ounces, had put on far less weight than the controls. None were obese.

Both exercise and portion control, in other words, had effectively protected the animals against their fated fatness.

But beneath the skin, the runners and the dieters looked very unalike. By almost all measures, the runners were metabolically healthier, with better insulin sensitivity and lower levels of bad cholesterol than the dieters. They also burned more fat each day for fuel, according to their metabolic readings, and had more cellular markers related to metabolic activity within their brown fat than the dieting group. Brown fat, unlike the white variety, can be quite metabolically active, helping the body to burn additional calories.

Interestingly, the runners also had developed different gut microbes than the dieters, even though they ate the same food. The runners had greater percentages of some bacteria and smaller populations of others than the dieters or the control group; these particular proportions of gut bugs have been associated in a few previous studies with long-term leanness in both animals and people.

Perhaps most striking, “the runners showed no signs of compensatory eating or compensatory inactivity,” said Victoria Vieira-Potter, an assistant professor of nutrition and exercise physiology at the University of Missouri who oversaw the study. They didn’t scarf down more food than the control group, despite running several miles every day and, according to the specialized cages, actually moved around more when not exercising than either of the other groups of rats.

In essence, the runners, while weighing the same as the dieters at the end of the study, seemed better set up to avoid weight gain in the future.

Of course, these were rats, which do not share our human biology or our tangled psychological relationships with food and body fat.

This study also involved young, normal-weight rodents and cannot tell us whether exercise or dieting alone or in combination would aid or hinder weight loss in people (or animals) who already are overweight, Dr. Vieira-Potter said. Metabolisms change once a body contains large amounts of fat, and it becomes increasingly difficult to permanently drop those extra pounds.

So better to avoid weight gain in the first place, if possible. And in that context, she said, “restricting calories can be effective,” but exercise is likely to be more potent in the long term and, of course, as common sense would tell us, doing both—watching what you eat and exercising—is best of all.

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Bodily Changes Are Driving Girls Out of Sports

Harriet Lee-Merrion

Spring, finally!

So why aren’t more teenage girls out on the playing fields?

Research shows that girls tend to start dropping out of sports and skipping gym classes around the onset of puberty, a sharp decline not mirrored by adolescent boys.

A recent study in The Journal of Adolescent Health found a surprisingly common reason: developing breasts, and girls’ attitudes about them.

In a survey of 2,089 English schoolgirls ages 11 to 18, nearly three-quarters listed at least one breast-related concern regarding exercise and sports. They thought their breasts were too big or too small, too bouncy or bound too tightly in an ill-fitting bra. Beginning with feeling mortified about undressing in the locker room, they were also self-consciously reluctant to exercise and move with abandon.

Experts on adolescent health praised the study for identifying and quantifying an intuitive thought.

“We make assumptions about what we think we know, so it’s important to be able to say that as cup size increases, physical activity decreases for a lot of girls,” Dr. Sharonda Alston Taylor, an assistant professor of pediatrics at Baylor College of Medicine in Texas, who focuses on adolescent obesity.

The challenge is what to do about it.

After reading the study, some pediatricians and adolescent health specialists said they needed to do a better job informing girls about breast health and development. Almost 90 percent of the girls in the study said they wanted to know more about breasts in general, and nearly half wanted to know about sports bras and breasts specifically with respect to physical activity.

Joanna Scurr, the lead author of the study and a professor of biomechanics at the University of Portsmouth in England, said the breast itself had little internal support, so when a girl’s body moved, the breast moved independently, and the movement increased with breast size. In up to 72 percent of exercising women, she said, that movement was a cause of breast pain or discomfort.

Yet while sports and physical education programs frequently recommend protective gear for boys, like cups, athletic supporters and compression shorts, comparable lists for young women rarely include a mandatory or even recommended sports bra.

Only 10 percent of the girls surveyed said they always wore a sports bra during sports and exercise. More than half had never worn one.

Dr. Taylor said that lack of education about bra fitting and sizing was commonplace in her practice.

“The mom will say, ‘I don’t know what size she is,’ and the patient will say, ‘I just grab my sister’s or my mother’s bras to wear.’”

Using data from this study and others, the researchers from sports and exercise health departments at three British universities are trying to design school-based educational programs.

When researchers asked the girls how they would prefer to receive breast information — via a website, an app, a leaflet or a private session with a nurse — the overwhelming majority replied that they wanted a girls-only session with a female teacher.

At what age? “Most of them said 11,” Dr. Scurr said.

Andria Castillo, now 17 and a junior at Mather High School in Chicago, says she remembers that when she was around that age, she was painfully self-conscious about her breast size; she thought she was developing more slowly than everyone else.

“I felt boys and girls were making fun of me,” she said. “Even though no one called me out, I felt they were, behind my back. I was taking taekwondo, and I would look in the big mirror and try to find ways to cover myself up and hide. I asked my dad if I could stop going.”

She had a friend who had been active in sports. But in the sixth grade, the girl’s breasts developed rapidly. “She eventually stopped going to gym altogether,” Ms. Castillo said. “Instead, she just went to a classroom and did her homework.”

In time, Ms. Castillo turned her attitude around; she is now on her school’s varsity water polo and swim teams. She credits not only her mother, but also a Chicago-based project, Girls in the Game, which has body-positive, confidence-building programs, including single-sex athletics.

Some experts in female adolescent obesity and fitness suggested that young girls would be more comfortable in single-sex gym classes. But others said that option had its disadvantages, too.

Kimberly Burdette, a doctoral candidate in psychology at Loyola University Chicago who looks at the psychological factors that promote well-being and healthy weight in girls, says such separation might be helpful at a time when adolescent girls had a heightened awareness that others were looking at their bodies.

“It’s hard to be in the zone, focusing on athletic movement, on what your body can do, if you’re thinking about what others think your body looks like,” she said. “I like programming that is for girls only, where a girl can try a sport, regardless of her ability, without the male gaze.”

But Elizabeth A. Daniels, an assistant professor of developmental psychology at the University of Colorado Colorado Springs, disagreed. “I’m not sure the concern or embarrassment is always just about boys,” she said, noting that girls can make derisive comments about one another. “So do we change the structure of the gym class or address respectful behavior?”

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1 Minute of All-Out Exercise May Equal 45 Minutes of Moderate Exertion

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For many of us, the most pressing question about exercise is: How little can I get away with? The answer, according to a sophisticated new study of interval training, may be very, very little. In this new experiment, in fact, 60 seconds of strenuous exertion proved to be as successful at improving health and fitness as three-quarters of an hour of moderate exercise.

Let me repeat that finding: One minute of arduous exercise was comparable in its physiological effects to 45 minutes of gentler sweating.

I have been writing for some time about the potential benefits of high-intensity interval training, a type of workout that consists of an extremely draining but brief burst of exercise — essentially, a sprint — followed by light exercise such as jogging or resting, then another sprint, more rest, and so on.

Athletes rely on intervals to improve their speed and power, but generally as part of a broader, weekly training program that also includes prolonged, less-intense workouts, such as long runs.

But in the past few years, exercise scientists and many of the rest of us have become intrigued by the idea of exercising exclusively with intervals, ditching long workouts altogether.

The allure of this approach is obvious. Interval sessions can be short, making them a boon for anyone who feels that he or she never has enough time to exercise.

Previously, I have written about a number of different interval programs, involving anywhere from 10 minutes of exhausting intervals in a single session to seven minutes, six, four and even fewer. Each program had scientific backing. But because of time and funding constraints, most studies of interval training have had limits, such as not including a control group, being of short duration or studying only health or fitness results, not both.

Consequently, fundamental questions have remained unanswered about just how well these very short, very intense workouts really stack up against traditional, endurance-style training.

So scientists at McMaster University in Hamilton, Ontario, who had themselves conducted many of those earlier studies of interval training, decided recently to mount probably the most scientifically rigorous comparison to date of super-short and more-standard workouts.

They began by recruiting 25 out-of-shape young men and measuring their current aerobic fitness and, as a marker of general health, their body’s ability to use insulin properly to regulate blood sugar levels. The scientists also biopsied the men’s muscles to examine how well their muscles functioned at a cellular level.

Then the researchers randomly divided the men into three groups. (The scientists plan to study women in subsequent experiments.) One group was asked to change nothing about their current, virtually nonexistent exercise routines; they would be the controls.

A second group began a typical endurance-workout routine, consisting of riding at a moderate pace on a stationary bicycle at the lab for 45 minutes, with a two-minute warm-up and three-minute cool down.

The final group was assigned to interval training, using the most abbreviated workout yet to have shown benefits. Specifically, the volunteers warmed up for two minutes on stationary bicycles, then pedaled as hard as possible for 20 seconds; rode at a very slow pace for two minutes, sprinted all-out again for 20 seconds; recovered with slow riding for another two minutes; pedaled all-out for a final 20 seconds; then cooled down for three minutes. The entire workout lasted 10 minutes, with only one minute of that time being strenuous.

Both groups of exercising volunteers completed three sessions each week for 12 weeks, a period of time that is about twice as long as in most past studies of interval training.

By the end of the study, published in PLOS One, the endurance group had ridden for 27 hours, while the interval group had ridden for six hours, with only 36 minutes of that time being strenuous.

But when the scientists retested the men’s aerobic fitness, muscles and blood-sugar control now, they found that the exercisers showed virtually identical gains, whether they had completed the long endurance workouts or the short, grueling intervals. In both groups, endurance had increased by nearly 20 percent, insulin resistance likewise had improved significantly, and there were significant increases in the number and function of certain microscopic structures in the men’s muscles that are related to energy production and oxygen consumption.

There were no changes in health or fitness evident in the control group.

The upshot of these results is that three months of concerted endurance or interval exercise can notably — and almost identically — improve someone’s fitness and health.

Neither approach to exercise was, however, superior to the other, except that one was shorter — much, much shorter.

Is that reason enough for people who currently exercise moderately or not at all to begin interval training as their only workout?

“It depends on who you are and why you exercise,” said Martin Gibala, a professor of kinesiology at McMaster University who oversaw the new study.

“If you are an elite athlete, then obviously incorporating both endurance and interval training into an overall program maximizes performance. But if you are someone, like me, who just wants to boost health and fitness and you don’t have 45 minutes or an hour to work out, our data show that you can get big benefits from even a single minute of intense exercise.”

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Getting People to Move More

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In 2010, a group of public and private organizations banded together to develop and release the first National Physical Activity Plan, a blueprint for getting Americans to move more.

Among its recommendations were that every schoolchild be allowed and encouraged to participate in frequent — and preferably daily — physical education classes; that employers find ways to reduce sitting time at the office; and that municipalities both create and promote parklands, bike paths and other places for people to be active.

But since the release of the plan, by an alliance that includes the American Heart Association, American Cancer Society, Centers for Disease Control and Prevention, and the Department of Health and Human Services, physical activity levels in the United States have barely budged, and for many people, they have declined. According to a recent report, only eight states require recess every day for elementary school students and only Oregon and the District of Columbia mandate that all children in elementary and middle school participate in at least 30 minutes of physical education every day, the minimum desirable level of daily P.E. that experts recommend.

Meanwhile, according to the C.D.C., barely 20 percent of American adults meet the minimum national exercise guidelines of at least 150 minutes per week of mixed aerobic workouts and strength training. The percentages are even lower for many minority groups, including Hispanic adults. Only about 15 percent of them manage to meet the exercise recommendations.

More disquieting, a health study published last month concluded that, over all, fewer than 3 percent of American adults live the kind of comprehensively healthy life that we all know we should, with a diet rich in fruits and vegetables, no smoking, a normal weight and regular exercise. Of these, the factor that was most likely to keep someone from joining the small group of health-wise Americans was exercise. Almost no one in the study did much.

In the face of this seemingly intractable tug toward physical stillness, the alliance today released a new National Physical Activity Plan, with updated priorities, a broader focus on minorities with the addition of a diversity committee, and more recommendations and advice for how people might encourage physical activity in their communities and schools.

To find out more about the new plan and why so many of us remain so resolutely sedentary, I spoke with Russell Pate, a professor of public health at the University of South Carolina in Columbia and chairman of the National Physical Activity Plan Alliance. Here are edited excerpts from our conversation.

Q.

The most obvious question about the National Physical Activity Plan is why do we need one? Why is it still so hard to get people to exercise, when we all know that we should?

A.

In fairness to people, we have made it so easy to be inactive. Once, stairs would have been the first thing that you saw in a building. Today, elevators are front and center. You have to hunt around for the stairs. And we can drive everywhere. In today’s world, it’s activity that is unusual, not inactivity. Being active requires commitment, and for some people, that commitment can seem too much. A single mother of three kids working two or three jobs may well feel like working out is a luxury that she can do without.

Q.

Is that why the plan emphasizes physical activity rather than exercise?

A.

Many people think of exercise as something that is planned and high-intensity and a lot of work. Physical activity is a more inclusive term. Any movement can be considered physically active and beneficial, even if you just walk around the house instead of sitting on the couch. We want to convey the idea that you don’t have to exercise, just move more.

Q.

But how, in a concrete way, can a national plan increase activity? How could someone use the plan to, for instance, get more P.E. classes added to the curriculum of their child’s elementary school?

A.

There is a section devoted to education. It includes a series of evidence-based strategies and tactics. You can find information there about why schools should meet national and state standards for physical education and how to accomplish that, such as encouraging shared-use agreements so that schools can use community facilities if they don’t have their own resources. This plan is meant to be practical. A parent could print out that section, take it to a school board meeting and say, ‘Look, I didn’t dream up the idea that we need P.E. It’s right here in the National Physical Activity Plan.’

Q.

Are you optimistic?

A.

We are swimming upstream. We know that. The social conditions that promote inactivity have been building for decades. It is so easy now not to move. But the consequences are also becoming more obvious. Inactivity is associated with so many health problems and premature death. I believe that as people consider what it means to have a high-quality life, there will be a shift in behavior. Do we want to spend our lives on the couch surrounded by empty pizza boxes? Sure, some people might. But I think that most of us want healthy workplaces, schools and homes. We want our children and loved ones and ourselves to be well. To achieve that, we must move more.

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