The effects of swimming exercise on bone mineral density in postmenopausal women

In this study, we investigated the effects of a 2-year swimming program on suppressing bone loss in postmenopausal women. There were 22 subjects who participated in the swimming program (mean age 59.5 yr) and 19 controls (mean age 59.3 yr). The program consisted of one-hour exercise sessions ; and the swimmers had on average 1.5 sessions per week. BMD at the lumbar spine (L2∼ L4) and proximal femur (neck, trochanter, and Ward's triangle) were measured by dual X-ray absorptiometry (DXA) ; and leg extensor power was measured using a dynamic leg extensor power rig. All the measurements were taken at baseline, 1 and 2 years. Height, weight, calcium intake and daily activity profiles were similar between the two groups, and these changed little throughout the experiment. In regard to leg extensor power, the swimming group had a significant increase at 1 and 2 years. At 2 year, the swimming group demonstrated 4.4%, 5.7% and 3.4% increases in BMD at the femoral neck, trochanter and Ward's triangle, respectively, while the control group showed slight decreases of BMD at the femoral neck (-0.2%) and Ward's triangle (-1.4%). Significant differences in the rate of change in BMD at each site were observed between the two groups. The swimming group showed a decrease in lumbar spine BMD, as did the control group and the rate of the decline did not differ between the two groups. This study suggests that a 2-year swimming program for postmenopausal women can induce the beneficial effects of retarding bone loss at the proximal femur site and increasing leg extensor power.