ABSTRACT
BACKGROUND: The strength of aging bone depends on the balance between the resorption and formation phases of the remodeling process. The purpose of this study was to examine the interaction of two factors with the potential to exert opposing influences on bone turnover, resistance exercise training and high dietary protein intake. It was hypothesized that resistance training by young, healthy, untrained women with protein intakes near recommended levels (0.8 g.kg(-1).d(-1)) would promote bone formation and/or inhibit bone resorption, and that subsequent supplementation to provide 2.4 g protein.kg(-1).d(-1) would reverse these effects. METHODS: Bone formation was assessed with serum bone-specific alkaline phosphatase (BAP) and osteocalcin (OC), and bone resorption with urinary calcium and deoxypyridinoline (DPD). Biochemical, strength, anthropometric, dietary, and physical activity data were obtained from 24 healthy, untrained, eumenorrheic women (18-29 y) at baseline, after eight weeks of resistance training (3 d.wk(-1), approximately 1 hr.d(-1); 3 sets, 6-10 repetitions, 13 exercises, 75-85% maximum voluntary contraction), and after 12 weeks of resistance training and 10 days of protein/placebo supplementation. Subjects were randomized (double-blind) to either a high protein (HP) or training control (TC) group and, during the final 10 days, consumed either enough purified whey protein to bring daily protein intake to 2.4 g.kg(-1).d(-1), or an equivalent dose of isoenergetic, carbohydrate placebo. RESULTS: Strength, lean tissue mass, and DPD increased significantly in both groups over time, while percent body fat and BAP decreased (repeated measures ANOVA, p < or = 0.05, Bonferroni correction). No significant changes were observed for serum OC or urinary calcium, and no significant group (TC, HP) x time (baseline, week 8, week 12) interactions emerged for any of the biochemical measures. CONCLUSION: (1) Twelve weeks of high-intensity resistance training did not appear to enhance bone formation or inhibit bone resorption in young adult women, as assessed by biochemical markers of bone metabolism. (2) Subsequent maintenance of a high protein intake for 10 days in these regularly-training, calcium-replete women also showed no effects on bone metabolism.
ABSTRACT
BACKGROUND: The purpose was to study the effects of age on body fluid distribution during exercise and exercise combined with heat stress. METHODS: Ten young (Y; 23.2 +/-0.7 yr) and eight older (O; 65.3 +/- 1.0 yr) men performed two 80-min intermittent exercise bouts on a cycle ergometer at 50% VO2peak, one in a thermoneutral (N), 22 degrees C environment, the other in a hot (H), 40 degrees C environment. For each condition, changes in serum protein, albumin, and electrolytes (Cl-, Na+, K+); total body water (TBW); plasma volume (PV); and interstitial (ISF), extracellular (ECF), and intracellular (ICF) fluids were determined. RESULTS: During exercise, [Cl-] responses increased more in O than Y (p < or = 0.05) while albumin (g) increased in Y and decreased in O (p < or = 0.05). There were no age-related differences in total protein changes nor any of the other blood parameters. PV decreased similarly for all subjects in both conditions with larger decreases in the H environment (241.8 +/- 40.3 vs. 478.3 +/- 46.0 mL). Loss of TBW was exacerbated in the H condition and significantly different (p < 0.05) between the groups (N: Y = -1.03 +/- 0.076 L, O = -0.88 +/- 0.12 L; H: Y = -1.65 +/- 0.12 L, O = -1.85 +/- 0.14 L). The O group lost more ICF (p < 0.05) (N: Y = -510.4 +/- 86.8 mL, O = -631.7 +/- 115.1 mL; H: Y = -529.3 +/- 118.0 mL, O = -928.6 +/- 118.9 mL) and less ISF (p < 0.05) (N: Y = -295.5 +/- 101.1 mL, O = 15.8 +/- 77.6 mL; H: Y = -684.6 +/- 134.5 mL, O = -397.9 +/- 165.5 mL) in both conditions. CONCLUSIONS: There was an interactive effect between age and heat stress in TBW loss. In addition, older individuals lost more ICF and less ISF than younger individuals during prolonged exercise. These findings suggest that the utilization of ICF, rather than ISF, to preserve PV during cycling exercise at or near 50% VO2max may be an age-related compensation.
