No additional effect of different types of physical activity on 10-hour muscle protein synthesis in elderly men on a controlled energy- and protein-sufficient diet

Purpose: The elderly lose skeletal muscle mass with age, which may be detrimental for function and quality of life. Both inactivity and heavy resistance exercise are known to have marked but opposite effects upon muscle mass. However, the potential effects of daily physical activity upon muscle protein synthesis (MPS) are less investigated. The aim of this study was to determine the effects of daily physical activities upon MPS in elderly individuals.

Methods: A total of 24 elderly men (70±1year) were recruited and randomly assigned: inactivity in form of bed-rest (IA), daily physical activities (DA), or heavy resistance exercise (RE). All groups undertook a normal eating routine containing carbohydrates (52 E%), fat (32 E%), and protein (16 E%). Ingestion of labeled milk protein ([1-(13)C]leucine-labeled whey and caseinate) served to maintain tracer enrichment for determination of 10-hour myofibrillar protein fractional synthesis rates (FSR), and typical prerequisites for calculating FSR were fulfilled. Physical activities were monitored, and venous blood and muscle biopsies collected.

Results: Physical activity was highest in the DA compared to both the IA and RE groups. Nutrient ingestion increased insulin, leucine, and phenylalanine plasma concentrations in all groups. [1-(13)C]leucine enrichment was stable throughout the 10-hour FSR period. Myofibrillar protein FSR were similar for IA, DA, and RE groups, 0.055±0.003%/h, 0.058±0.006%/h, and 0.065±0.008%/h, respectively (means±SE, P=0.44).

Conclusions: In elderly males, inactivity, daily activities, and resistance exercise interventions result in equal 10-hour, whole day MPS during an energy- and protein-sufficient diet regimen.