Healthy Kids Chuck Corbin

Most Americans are aware of the health benefits of physical activity. The evidence indicates that regular exercise reduces the risk of chronic diseases such as heart disease, diabetes, various forms of cancer, and depression.

Most are aware that regular “load bearing” exercise can increase bone mass and reduce the risk of osteoporosis (low bone density leading to risk of fracture). Load bearing exercises are those that stress the long bones such as walking and jogging (load equals body weight) and resistance exercise (load equals weights). Guidelines for adults, especially older adults, recommend walking and resistance exercise to reduce risk of bone loss as we age.

Many Americans, however, are not aware of the fact that regular load bearing exercise is important during childhood and adolescence. A recent comprehensive review in Exercise and Sport Sciences Reviews (ESSR) presents compelling evidence that activity in youth has benefits for the bones, both immediately, and throughout life.

At birth our bones are soft, but as we age, the bones become more dense (harder). Peak bone density refers to the highest density of the bones at any point in life. Peak bone density is typically achieved during the teens or early 20s. Approximately 40 percent of our bone mass is achieved during the two years before and two years after the growth spurt in adolescence. As we age, the density of the bones gradually decreases. If bone density decreases too much we have osteoporosis. Activity during youth can build “a bank” of peak bone density on which you can draw throughout life. Continued regular exercise throughout life can reduce bone loss and keep bone density above the osteoporosis threshold.

So what is recommended for children and teens? The authors of the ESSR support the national guideline that recommends at least 60 minutes of daily physical activity for youth. Walking, jogging, skipping and other similar movement activities are a good start. Calisthenics and muscle fitness exercises that meet youth guidelines are also good. Jumping activities (sports that involve jumping) have been shown to be especially effective in building the bones. The research indicates that the most effective programs have been school-based programs that include moderate to vigorous activities such as those described above. These finding provide evidence to support school physical education and sports programs, as well as community sports programs for youth.

The most basic principle of exercise is the overload principle. If you overload the muscles and bones, it makes them stronger. If you are sedentary, you lose muscle and bone. You use it or you lose it! Exercising to build the bones in youth provides bone density that can reduce risk of low bone density later in life.

• Ahwatukee Foothills resident Dr. Charles B. “Chuck” Corbin is professor emeritus at Arizona State University, author of more than 90 books on fitness and activity, and was the first chair of the President’s Council on Physical Fitness, Sports, and Nutrition Science Board. For more information on the National Physical Activity Guidelines for Americans, go to

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