People who regularly run or walk briskly appear to have healthier discs in their spines than people who do not exercise, according to one of the first studies to closely examine links between movement and disc health.
The findings refute a widely held belief that activities like running might overtax the spine and indicate that, instead, they make it sturdier.
The human spine is a complicated mechanism, composed of vertebral bones cushioned between intervertebral discs. These discs, shaped like tiny whoopee cushions, contain a viscous fluid that compresses and absorbs pressure during movement, keeping the back in good working form.
With age, disease or injury, spinal discs can degenerate and bulge, resulting in back pain, which can be debilitating.
Until recently, scientists and clinicians had believed that people could do little to strengthen their spinal discs, although they obviously could injure them. Muscles and bones respond to the physical strains of movement by becoming larger and stronger. But most experts thought that spinal discs remain impervious to this process and might in fact be harmed by the jarring from running.
There were tantalizing hints in animal studies, however, that this idea could be out of date. When scientists in Sweden scanned the spines of mice before and after they ran for several weeks on treadmills, the researchers noticed significant increases in the size of their spinal discs, indicating that those structures had been responding and adapting to the demands of running.
But mice, of course, run on four legs and are in all other respects not people, and it remained unclear whether running and similar activities would be good or not for the human spine.
So for the new study, which was published in April in Scientific Reports, researchers at Deakin University in Australia and other institutions decided to examine the backs of people who run and others who do not.
Eventually they recruited 79 adult men and women, two-thirds of whom said that they were runners. Some of these told the researchers that they covered more than 30 miles (about 50 kilometers) a week in training. The researchers designated these as the “long-distance” group. The others said that they ran between 12 and 25 miles a week. All had been training for at least five years.
The final group rarely exercised at all.
To ensure that people’s reported activity levels were accurate, the researchers asked their volunteers to wear accelerometers for a week.
Then they scanned everyone’s spines, using a sophisticated type of M.R.I. that precisely measures the size and liquidity of each disc.
And they found differences. In general, the runners’ discs were larger and contained more fluid than the discs of the men and women who did not exercise.
Since both greater size and increased levels of internal fluid indicate better disc health, the runners harbored fundamentally healthier spines than the people who were sedentary, says Daniel Belavy, a professor of physical activity and nutrition at Deakin University who led the study.
Interestingly, mileage barely mattered. The discs of the people who ran less than 30 miles per week were almost identical to those in the long-distance group, suggesting that, compared to moderate mileage, heavy training does not augment disc health but also does not contribute to deterioration.
Still, the researchers wished to gain more specificity about the ideal level of exercise for disc health and so began rooting deeper into their accelerometer data. Accelerometers measure movement in terms of acceleration forces, or how much power your body is generating when you move.
The researchers soon pinpointed a narrow range of forces that were associated with the healthiest discs.
They then asked 10 of their volunteers to step onto treadmills and recreate these forces and found, to their surprise, that running was not required. Walking briskly at a pace of about four miles per hour — “which for some people would be a jog,” Dr. Belavy says — generated enough physical force to bring people’s movement into the range associated with the healthiest discs.
Slower walks and standing in place were outside this range, as were runs at paces beyond about 5.5 miles per hour. The sweet spot for disc health seemed to reside somewhere in the range of fast walks and gentle jogs.
“You can go running” for the sake of your back, Dr. Belavy concludes, “but you don’t have to.” A brisk walk will also help, it seems.
Of course, this was a one-time snapshot of people’s backs. It cannot prove that exercise caused people’s discs to become healthier, but only that people who ran had healthier discs.
It also does not tell us whether exercise might aid in treating existing disc problems.
Dr. Belavy and his colleagues hope to delve into those issues in future randomized experiments.
But for now, he says, the available evidence strongly indicates that “discs like movement,” and it would be worthwhile to take your back for a walk today.