Exercise has many benefits, but it does not build strong bones. Tara Moore/Getty Images
Misconception: All you have to do is walk or do modest strength training exercises to build strong bones.
Actually: Exercise has little or no effect on bone strength.
It sounded too good to be true, and, unfortunately, it was.
Many public health groups, professional societies and health sites on the Internet promote this exercise prescription, promising it will stave off weak bones.
But osteoporosis researchers know the advice is not backed up by rigorous studies.
The idea may have begun as an extrapolation of a well-known fact: People who are bedridden lose bone mass. So do astronauts who spend time weightless.
The pull of gravity seems to be needed for bone strength. But is there a threshold beyond which bones are about as strong as they will be from the force of gravity? Is everyday walking around just as good as running a marathon? Those studies did not say.
The answer came a little more than a decade ago when scientists did rigorous studies, asking if weight bearing exercise increased bone density in adults.
They used DEXA machines, which measure bone density by hitting bones with X-rays.
Those studies failed to find anything more than a minuscule exercise effect — on the order of 1 percent or less, which is too small to be clinically significant.
As expected, DEXA found bone loss in people who were bedridden and in astronauts. But there was no evidence that bone was gained when people walked or ran.
Scientists have continued to investigate as tests for bone density grow ever more sensitive.
More recently, using new and very expensive machines that scan bone and are able to show its structure at a microscopic scale, they reported a tiny exercise effect in one part of the bone’s architecture known as the trabecula, little branches inside bone that link to each other.
The cortical shell — the outer layer of bone — also seems to be slightly thicker with weight bearing exercise.
But these are minute changes, noted Dr. Clifford Rosen, a bone researcher at the Maine Medical Research Institute.
There is no evidence that they make bone stronger or protect it from osteoporosis, he said.
All that can be said is that if exercise builds bone, it does not build much bone.
Which isn’t to say that exercise cannot protect bones in other ways.
Studies have found that older people who did weight bearing exercise decreased their risk of fractures.
But this seems to be more likely explained by the fact that exercise leads to stronger muscles that in turn made falling less likely.
At this point nothing except injections of parathyroid hormone and, perhaps, a new injectable drug called abaloparatide now being tested in clinical trials, make bone denser and stronger.
Popular osteoporosis drugs like Fosamax slow the rate of bone loss, but they do not build bone.
There is a glimmer of hope for those who have put their faith in exercise.
Perhaps, osteoporosis researchers say, even though bones do not get stronger with exercise, exercise might make bones healthier in terms of a mysterious property called bone quality.
No one knows exactly what it is but it may help explain why some people with bones that look strong get fractures while others with bones that look fragile do not.
Maybe those microscopic changes in bone make a crucial difference, but it is too soon to say.
Original Article: Exercise Is Not The Path To Strong Bones
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