Daily living physical activities and muscle protein synthesis: a new and applied method with intrinsically stable isotope‐labeled milk proteins as tracer (702.8)

Abstract

Aims of this study were to evaluate effects of daily physical activities on muscle protein synthesis (MPS) and to validate a tracer protocol with intrinsically labeled milk proteins. 24 elderly (70 ± 1 y) men were recruited and randomly assigned to: inactivity (IA), daily activities (DA), or strength exercise (SE). The study protocol simulated a normal daily eating routine containing carbohydrates, fat, and [1‐13C]leucine‐labeled whey and caseinate as the primary protein source. Regular ingestion of labeled protein served to prime (whey) and maintain (caseinate) tracer enrichment for determination muscle protein fractional synthesis rates (FSR). Physical activities were monitored and venous blood and muscle biopsies collected. Total physical activity was highest in DA compared to IA and SE. Protein ingestion increased leucine and phenylalanine plasma concentrations in all groups. Plasma [1‐13C]leucine enrichment was stable throughout the 10‐h FSR measurement period. Muscle protein FSR were for IA, DA, and SE 0.065 ± 0.0050 %/h, 0.077 ± 0.0081 %/h, and 0.081 ± 0.0057 %/h, respectively (means ± SE, one‐way ANOVA P = 0.199). The prerequisites for calculating FSR was fulfilled with the tracer coming solely from oral intake of milk proteins. Under these applied settings it was not possible to detect significant differences in MPS between the inactivity, daily activities, and strength exercise interventions.Grant Funding Source: Supported by Arla Foods Ingredients P/S and Lundbeck Foundation