Exercise in youth makes for stronger, bigger bones through life

Date: Mar-26-2014Our bone is living tissue that responds to the forces that act on it - it gets

stronger when we exercise. Now a new study suggests exercising when young helps bones grow big

and strong for life, and that this effect persists during aging.

To arrive at this finding, researchers compared the differences between the throwing and

non-throwing arms of major league baseball players measured at different points in their careers

to differences measured in non-baseball players.

They found that half of the bone size and one-third of the bone strength benefit of exercise

performed during youth persisted throughout life.

Lead author Stuart Warden, an associate professor at Indiana University-Purdue University

Indianapolis, says:

"This is an impressive level of maintenance, particularly considering that the baseball

players had not thrown, or in other words, exercised, in over 50 years and were aged in their

mid-80s."

The researchers were not, however, surprised to find that the amount or mass of new bone

added as a result of exercising during youth was gradually lost as the players aged.

Prof. Warden says it is "not energy efficient for the skeleton to maintain its mass in excess

of its needs."

As we age we lose bone from the inside

But Prof. Warden and his colleagues were still intrigued by the question - how can exercise during

youth have a lifelong benefit on bone strength but not bone mass?

You can strengthen any load-bearing structure by adding more mass, especially where it is

needed most. And bone is no different, as Prof. Warden explains:

"Exercise during youth adds extra layers to the outer surface of a bone to essentially make

the bone bigger. This gives you more 'bang for the buck,' as the addition of a small amount of

new material to the outside of a bone results in a disproportionate increase in bone strength

relative to the gain in mass."

But as we age, we lose bone mostly from the inside, not the outside. Prof. Warden says this

means the bigger and stronger bone that amasses as a result of exercising in younger years

endures for a lifetime.

Exercising later in life also benefits bone health

Prof. Warden says children should exercise for at least an hour a day, and at least a third of that

time should be devoted to weight-bearing exercise such as running.

The other question this raises is does exercising later in life make a difference to the

aging skeleton?

According to Prof. Warden the answer is "yes," because of tests they conducted on retired

major league baseball players.

The retired players were in two groups. In one group the players had completely stopped

throwing when their professional baseball careers ended, and in the other group, the retired

players had continued to throw for another 20 years after the end of their professional

careers.

The results showed that continuing exercise during aging did not make bones bigger, but it

did prevent loss of bone from the inside, as Prof. Warden notes:

"The net result was the maintenance of even more of the strength benefit of exercise

completed during youth, with baseball players who continued to throw during aging maintaining

over 50 percent of the bone strength benefit of exercise performed in youth."

He says the data suggests the idea of "use it or lose it" does not necessarily apply to the

skeleton, and we should encourage exercise in youth, while bodies are still growing, as a way to

promote bone health for life.

Prof. Warden says children should exercise for at least an hour a day, and at least a third of that

time should be devoted to weight-bearing exercise such as running, jumping rope, tennis, soccer,

basketball, volleyball and hopscotch, where forces act on the skeleton from different

directions.

He adds that by continuing to exercise into old age we hold onto much of the bone health

gains we generated when we were younger. It also ensures we maintain muscle strength and balance

and reduce our chances of falling.

The study was funded by the National Institutes of Health and is published in the Proceedings of the National Academy of Sciences.

Meanwhile, Medical News Today recently reported a study that shows how much of bone comprises shock-

absorbing 'goo' that stops it shattering. The UK researchers say the finding will shift the

way we think about bone diseases like osteoporosis.

Written by Catharine Paddock PhD




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