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There were tantalizing hints in animal studies, however, that this idea could be out of date.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.