A friend sent me this article that talks about an exercise effect that is rarely discussed: changes to our bones.
The short version of the article is that sprinters tend to develop thicker shins and tennis players can develop a thicker racquet arm, while swimmer’s and cyclists tend to have no such effect. The article also notes that children who walk sooner have thicker shins than those who walk later. The other side is true as well, which is why astronauts lose bone mass while in space.
This is Wolff’s Law in action. In a nutshell, Wolff’s Law states that if the body feels it is not set up to continue to support the pressure it is put under, it will create new bone to help. We can see this in the feet of ballet dancers, and in the pelvic shape of teenage girls who play sports. Sometimes these changes are not the result of exercise, but of daily living. People with obesity develop thicker femoral heads (the top of the thigh). Yet another example of how amazing the human body is!
The article notes that this effect is smaller in older populations, suggesting that studies have not shown large changes in bone mineral density in the elderly. The author suggests this may be because we can’t produce as much force as we age. This is an interestingly timed comment for me, as I just had a client report back to me this week that her rheumatologist reported that her bone mineral density has increased again – the second time she has had an increase since starting strength training with me.
I found myself questioning the conclusion that the effect is smaller in seniors. I followed the link in the article for “elderly people”, which led to this study abstract which makes no mention of smaller effects in seniors. It does mention that “the effects of age and starting age on the osteogenic effects of exercise are not well known. It also appears that exercise interventions are most effective in physically inactive people or counteracting conditions of disuse such as bed rest”. I would argue that suggests that they don’t really know the effect on seniors, but if we’re talking about inactive seniors, the study suggests a big potential impact on bone strength.
In fact this US Physical Activity Guidelines Advisory Committee Report from 2008 provides a review of studies on the topic. The results very clearly show improvement in bone mineral density (BMD) among seniors, including one to two percent increase in lumbar spine density per year from resistance training. From the report: “Although a benefit of 1 to 2 % per year may seem small, this is roughly equivalent to preventing the decrease in BMD that would typically occur over 1 to 4 years in postmenopausal women and elderly men”. 
As my friend who sent me the article said, “Like I needed another reason but really drives home the importance of an active lifestyle for kids- impacts the rest of their lives.”
In other words: walk away from the computer and go run, jump, play, or lift weights. Just tell your boss it’s a crucial medical intervention.
Elsbeth Vaino is an engineer turned personal trainer in Ottawa who loves discussing the geeky reasons for exercising. In fact if you’re a personal trainer on the west coast, consider coming to see me speak at the NSCA BC Provincial Clinic on May 28th. I’ll be talking about structural variations between individuals and their effect on exercise.