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Bone mass and muscle strength in female college athletes (runners and swimmers).

OBJECTIVE
To determine whether female college athletes had increased muscle strength and bone mass in comparison with age-matched nonathletic female subjects and, if so, whether participation in weight-bearing versus non-weight-bearing exercise made a difference.


MATERIAL AND METHODS
We performed a comparative statistical analysis of the bone mineral density (BMD) of the total body, lumbar spine, and femoral neck, maximal oxygen uptake (VO2max), muscle strength, and level of physical activity in 21 runners, 22 swimmers, and 20 control subjects. The study participants were female college students, 18 to 24 years old, who had had more than 8 normal menstrual cycles during the past year.


RESULTS
Statistical analyses showed significantly higher VO2max in the two athletic study groups than in the control subjects (P < 0.0001). No significant difference in BMD was noted among the three groups. Total body BMD (r = 0.30; P = 0.02) and femoral neck BMD (r = 0.39; P = 0.002) were positively correlated with weight-bearing activity but not with non-weight-bearing activity. VO2Max (an index of physical fitness) was positively correlated with femoral neck BMD (r = 0.33; P = 0.009) and trochanteric BMD (r = 0.29; P = 0.021). Shoulder muscle strength (determined by isokinetic dynamometry) was positively correlated with total body BMD (r = 0.34; P = 0.007) and lumbar spine BMD (r = 0.28; P = 0.028). Swimmers had higher muscle strength in the back and upper extremities than did runners and control subjects. Hip girdle muscle strength was not significantly different among the three groups. Total body BMD had a positive correlation with percentage of body fat and height. Lumbar spine BMD was higher in subjects who had previously used oral contraceptives. The athletes had a lower percentage of body fat, were less likely to have used oral contraceptives, and had fewer years of normal menses than did the control subjects.


CONCLUSION
Our study shows that (1) total body BMD and femoral neck BMD were significantly higher in the study group that performed weight-bearing exercises than in control subjects, (2) swimming exercise had no effect on BMD, and (3) although swimming is not a bone-building exercise, it can significantly improve shoulder, back, and grip muscle strength.