PROSPECTIVE 10-MONTH EXERCISE INTERVENTION IN PREMENARCHEAL GIRLS - POSITIVE EFFECTS ON BONE AND LEAN MASS

Enhancement of bone mineral acquisition during growth may be a useful preventive strategy against osteoporosis. The aim of this study was to explore the lean mass, strength, and bone mineral response to a 10-mo nth, high-impact, strength-building exercise program in 71 premenarche al girls, aged 9-10 years. Lean body mass, total body (TB), lumbar spi ne (LS), proximal femur (PF), and femoral neck (FN) bone mineral were measured using the Hologic QDR 2000+ bone densitometer. Strength aas a ssessed using a grip dynamometer and the Cybex isokinetic dynamometer (Cybex II). At baseline, no significant difference in body composition , pubertal development, calcium intake, physical activity, strength, o r bone mineral existed between groups. At completion, there were again no differences in height, total body mass, pubertal development, calc ium intake, or external physical activity. In contrast, the exercise g roup gained significantly more lean mass, less body fat content, great er shoulder, knee and grip strength, and greater TB, LS, PF, and FN BM D (exercise: TB 3.5%, LS 4.8%, PF 4.5%, and FN 12.0%) compared with th e controls (controls: TB 1.2%, LS 1.2%, PF 1.3%, and FN 1.7%). TB bone mineral content (BMC), LS BMC, PF BMC, FN BMC, LS bone mineral appare nt density (BMAD), and FN bone area also increased at a significantly greater rate in the exercise group compared with the controls. In mult iple regression analysis, change in lean mass was the primary determin ant of TB, FN, PF, and LS BMD accrual. Although a large proportion of bone mineral accrual in the premenarcheal skeleton was related to grow th, an osteogenic effect was associated with exercise. These results s uggest that high-impact, strength budding exercise is beneficial for p remenarcheal strength, lean mass gains, and bone mineral acquisition.