Bioeconomics. Why muscles get smaller and bones get thinner

Philip J. Goscienski, M.D.

December 2009

A person who has suffered a broken leg usually gets a rude awakening when the plaster cast — or perhaps fiberglass in this modern era — is removed. The skin is scaly and possibly a little malodorous but the real surprise is how much thinner the leg has become within the cast. Microscopic examination of the bone at a distance from the fracture site would show that it is considerably less dense than its mate.

What happens within a cast in 6 weeks is what happens to the muscles and bones of most persons in 60 years. It's as if nature chooses not to feed a structure that isn't doing any work. Welfare may be acceptable in the social scene but not in biology. In medical terms this is known as disuse atrophy and it too has eventual social significance: we all pay for it.

Since the earliest part of the 20th century American ingenuity has excelled in the development of labor-saving devices — a disaster in disguise. Barely 20 percent of us now get enough exercise to avoid losing muscle and adding fat. But that's not the end of the story. When muscles lose mass and strength they no longer pull as hard against bone. Relieved of physical stress and tension, bone becomes thin-walled, less dense and even changes its shape to a more rounded, weaker form. The result is osteoporosis.

Wasted muscles eventually lose nerve endings that help us to maintain balance. Older persons shuffle because they don't have enough strength in their legs to pick up their feet. Without good balance it's hard for them to stay upright when they stumble. Thin bones break easily, setting the stage for what has become an enormous health burden, a virtual epidemic of hip fractures.

Several factors contribute to osteoporosis, including unlucky genes and poor nutrition but a lack of physical activity is probably the most important. Exercise is most crucial in the years between the start of kindergarten and the end of college, a bone-building window that cannot be fully reopened once it has closed.

In spite of this, osteoporosis is not inevitable. Moderately intense weight-bearing activity can slow down bone loss enough in most people to avoid future fractures. Good nutrition, including calcium, other minerals, vitamins A, C, D and K and omega-3 fats are important. Side benefits include a much lower risk of heart disease, stroke and diabetes. Not a bad trade-off.

Philip J. Goscienski, M.D. is the author of Health Secrets of the Stone Age, Better Life Publishers 2005. Contact him at