Differential effects of swimming versus weight-bearing activity on bone mineral status of eumenorrheic athletes

Abstract

To examine the role of skeletal loading patterns on bone mineral density (BMD), we compared eumenorrheic athletes who chronically trained by opposite forms of skeletal loading, intensive weight-bearing activity (gymnastics, n = 13), and nonweightbearing activity (swimming, n = 26) and 19 nonathletic controls. BMD (g/cm) of the lumbar spine, femoral neck, trochanter, and whole body was assessed by dual energy X-ray absorptiometry (DXA). Subregion analysis of the whole body scan permitted BMD evaluation of diverse regions. Swimmers were taller (p = 0.0001), heavier (p > 0.005), and had a greater bone-free lean mass (p < 0.001) than gymnasts and nonathletic controls. When adjusted for body surface area, there was no difference in lean mass between swimmers and gymnasts, and both were higher than controls (p < 0.01). Gymnasts had a lower (p > 0.005) fat mass than swimmers and controls. There were no group differences for spine or whole body BMD, but gymnasts had higher spine BMD corrected for body mass than either swimmers or controls. Gymnasts (1.117 ± 0.110) had higher femoral neck BMD than controls (0.974 ± 0.105), who were higher than swimmers (0.875 ± 0.105) (p = 0.0001). This result still applied when BMD was normalized for body weight and bone size. Trochanter BMD of gymnasts (0.898 ± 0.130) was also higher than controls (0.784 ± 0.097) and swimmers (0.748 ± 0.085) (p = 0.0002), and remained higher when corrected for body mass. Whole body BMD normalized for body mass or bone size was significantly higher in gymnasts than in swimmers. Subregion analysis revealed arm BMD of gymnasts was greater than swimmers and controls (p > 0.01), and gymnasts' leg BMD was higher than that of swimmers (p > 0.05). These results suggest that the intensive weight-bearing activity characteristic of gymnastics is a powerful osteogenic stimulus and that long-term nonweightbearing training that incorporates forceful muscular contractions, as in swimming, confers no beneficial skeletal effects on bone mass of young women.