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Exercise and Bones: Lessons Learned from Female Athletes *

The ability of an athlete, female or male, to push her or his body to the physiologic limits has produced an extensive body of knowledge about how various physiologic systems respond to exercise. Although Wolff's Law (that change in the form or function of bone leads to change in internal structure) has long been a familiar tenet in orthopaedics, it was only recently that it was brought to bear on the problem of how to prevent or delay the bone loss that leads to osteoporotic fractures. Evidence for the effectiveness of mechanical loading on bones via physical activity falls into four categories: 1) cross-sectional studies of athletes and nonathletes, 2) prospective physical training studies documenting the effect of increased activity on bone, 3) correlational studies examining the relationship of bone mass or bone density and some measure of physical activity, and 4) epidemiologic studies looking at the activity histories of men and women with and without fractures. Most of the studies involving athletes fall into Category 1, where the effect of years of training and competition on the skeleton is most evident. Changes in the reproductive system experienced by a number of female athletes has also entered the picture and brought into question the belief of many women that exercise or exercise plus calcium could substitute for hormone replacement therapy in preserving their bones after menopause. Athletes who experience amenorrhea, oligomenorrhea, and perhaps even a short luteal phase have a lower bone mineral density than their eumenorrheic peers, which raises a question about the effectiveness of exercise in preventing bone loss in the hypoestrogenic woman.