Can Bone Loss Occur From High Aerobic Exercise?

Exercises that work against gravity place enough stress on your skeleton to stimulate the renewal of bone tissue. Sports that reduce gravitational stress during exercise can lead to weakening of the bones. If you focus entirely on high-intensity training in low-stress sports, you can gain fitness but develop bone structure weaker than that of a sedentary person. Cross-training in other sports replaces the essential stresses your skeleton needs for good health.

Beneficial Stress

The type of stress that exercise produces determines whether the training causes bone to become stronger or weaker. Your body constantly tears down and rebuilds bone tissue, redesigning bone to meet your physical needs. Without exercise, the internal structure of your bones weakens. New bone forms in response to repeated stress at levels above those you encounter in daily life. Lack of exercise and a drop in hormone levels as you age can cause osteopenia, a loss of bone density that precedes the brittle bones of osteoporosis. Not all intensive exercise generates the right sort of stress to maintain bone strength.

Low-Stress Sports

If you lift a heavy weight, many bones in your skeleton take the load. If you move the pedals of a bicycle faster, you stress very few bones. If you swim, your buoyancy takes gravitational stress off your skeleton completely. Both cyclists and swimmers can gradually lose bone density. In a study published in "Osteoporosis International" in 2003, master cyclists rode an average of 12.1 hours per week but did no weight-bearing exercise. Nonathletes exercised an average of 4.5 hours per week and included activities such as running, tennis and resistance training in their fitness programs, as well as cycling. Sixty-six percent of master cyclists showed bone loss in the lumbar spine and four showed symptoms of osteoporosis. Only 42 percent of the non-athletes showed osteopenia of the lumbar spine, and none suffered osteoporosis.

Correct Exercise

To prevent cycling or swimming from weakening your bones, cross-train in other activities that enhance bone strength. Working against gravity when you run or jump creates the right kind of stress, and strength training uses muscle power to stress supporting bones. Repeated pressure changes inside your bones trigger bone growth, according to an article in the "Journal of Aging Research" in 2011. Brief rests allow pressure to return to normal, resetting that essential pressure cycle. Learn new movements and new workouts occasionally to increase the positive effects on your bone strength. Bones that don't receive new stress don't benefit.

Amenorrhea

If you're both a highly trained athlete and a woman of child-bearing age, any intense physical training combined with poor diet could cause amenorrhea, the absence of menstruation. If you miss periods, see your doctor first but also consult with your coach. Amenorrhea signals a disruption in estrogen production and puts you at increased risk for osteoporosis. As many as 44 percent of female athletes experience exercise-associated amenorrhea, according to professor emeritus Ninfa S. Springer of the University of Michigan. Easing your training schedule and improving your diet often correct the problem by allowing weight gain and a return to health.