Effect of energy restriction on substrate utilization: muscle function and myofibrillar protein degradation in sedentary males and athletic females

An oxidative preference for fat or carbohydrate substrates has an impact on muscle protein metabolism. This study investigated how changes in substrate oxidation (through dieting) influences muscle function and contractile protein profiles. Eight sedentary males (Age:22 ± 1 years; Height: 175.9 ± 1.1 cm; Weight: 84.2 ± 2.9 kg) were placed on a diet and exercise program for 14 days where total energy deficit was 33% (22% from diet; 11% from exercise). All meals were consumed at the study center. Subjects jogged for 0.5 hours/day. Muscle biopsies and quadriceps muscle group function tests (Kin-Corn isokinetic dynamometer) were completed pre- and post-treatment Body weight decreased (1.5 ± 0.3 kg; p < 0.01) and fat oxidation increased (p < 0.05). Concentric average torque was lower (p < 0.05) at a movement velocity of 30 degrees/second. Myofibrillar proteins treated with a non-lysosomal protease, calpain, showed no increase in calpain activity within myofibrils. To test the hypotheses in an active population, this study was repeated in athletic females. Fourteen endurance athletes (Age:27 ± 2 years; Height: 167.2 ± 1.6 cm; Weight: 61.8 ± 1.9 kg; VC»2 max: 49.0 ± 0.9 ml/min/kg) were randomly assigned to maintenance energy (100% kcal) or energy restricted (75% kcal) diet groups. Subjects exercised for 100 minutes/day (within their normal exercise routine). Among the 75% diet group, body weight decreased (1.7 ± 0.3 kg; p < 0.05) and fat oxidation increased (p < 0.05). Peak concentric torque was significantly lower (p < 0.05) for the 75% diet group at 120 degrees/second, while average eccentric torque was significantly larger (p < 0.05) at 180 degrees/second. There were no significant changes in myofibrillar calpain activity in both diet groups. Results obtained from both groups suggest that increased fat oxidation induced by energy restriction was not conclusively related to changes in myofibrillar calpain activity. There were also no changes in quadriceps muscle function due to inconsistent trends within both sets of data. Indirectly, elevated calpain activity may be related to decreased muscle function since lack of changes in calpain activity was associated with no changes in muscle function. However, a direct effect of calpain activity on muscle function remains to be demonstrated.Land and Food Systems, Faculty ofGraduat