Lean body mass and weight-bearing activity in the prediction of bone mineral density in physically active men.

Weight-bearing endurance activity and resistance exercise are recommended to help preserve bone health during adulthood. However, the effects of resistance training relative to those of weight-bearing endurance activity often are confounded by body weight and composition. The purpose of this study was to determine the effects of long-term running, cycling, and resistance training on whole-body and regional bone mineral density (BMD), adjusting for body weight and composition. Cyclists (CYCLE; n = 19), runners (RUN; n = 10), and resistance trained men (RT; n = 13) ages 19-45 years participated in this cross-sectional study. Current and lifetime bone loading was calculated using ground-reaction force values of the reported physical activities. Whole-body and regional BMD and body composition were assessed using dual X-ray absorptiometry. Bone turnover markers and hormones were measured in fasting serum samples. The RT athletes had significantly greater body weight, lean body mass (LBM), and fat mass than CYCLE and RUN athletes; percent body fat did not differ among groups. Unadjusted BMD at all sites was significantly greater in the RT compared with CYCLE and RUN. After adjusting for LBM, RUN had significantly greater spine BMD than CYCLE. Subjects' LBM was a significant predictor of BMD in RT and CYCLE but not in RUN, suggesting that high-impact activity may override the benefits of LBM on BMD. Current bone loading was positively associated with serum osteocalcin concentrations (r = 0.480, p = 0.002). In conclusion, the results of the present study demonstrate that long-term running and resistance training increase BMD compared with cycling. However, it seems that high-impact activities, such as running, have a greater positive effect on BMD than resistance training.

Effect of a carbohydrate-protein supplement on endurance performance during exercise of varying intensity.

Increasing the plasma glucose and insulin concentrations during prolonged variable intensity exercise by supplementing with carbohydrate has been found to spare muscle glycogen and increase aerobic endurance. Furthermore, the addition of protein to a carbohydrate supplement will enhance the insulin response of a carbohydrate supplement. The purpose of the present study was to compare the effects of a carbohydrate and a carbohydrate-protein supplement on aerobic endurance performance. Nine trained cyclists exercised on 3 separate occasions at intensities that varied between 45% and 75% VO2max for 3 h and then at 85% VO2max until fatigued. Supplements (200 ml) were provided every 20 min and consisted of placebo, a 7.75% carbohydrate solution, and a 7.75% carbohydrate/1.94% protein solution. Treatments were administered using a double-blind randomized design. Carbohydrate supplementation significantly increased time to exhaustion (carbohydrate 19.7 +/- 4.6 min vs. placebo 12.7 +/- 3.1 min), while the addition of protein enhanced the effect of the carbohydrate supplement (carbohydrate-protein 26.9 +/- 4.5 min, p < .05). Blood glucose and plasma insulin levels were elevated above placebo during carbohydrate and carbohydrate-protein supplementation, but no differences were found between the carbohydrate and carbohydrate-protein treatments. In summary, we found that the addition of protein to a carbohydrate supplement enhanced aerobic endurance performance above that which occurred with carbohydrate alone, but the reason for this improvement in performance was not evident.