Our 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.