An abundant supply of amino acids enhances the metabolic effect of exercise on muscle protein

TLDR

Six untrained men received a 3‑hour intravenous infusion of a balanced amino‑acid mixture (≈0.15 g kg⁻¹ h⁻¹) at rest and after a leg resistance exercise bout, while muscle protein kinetics and amino‑acid transport were quantified from arteriovenous blood samples and muscle biopsies using an isotopic model. The infusion raised arterial amino‑acid concentrations similarly at rest and after exercise, but exercise increased leg blood flow, amino‑acid transport (30–100 % higher), and muscle protein synthesis (291 % vs.

Abstract

Six normal untrained men were studied during the intravenous infusion of a balanced amino acid mixture (approximately 0.15 g.kg-1.h-1 for 3 h) at rest and after a leg resistance exercise routine to test the influence of exercise on the regulation of muscle protein kinetics by hyperaminoacidemia. Leg muscle protein kinetics and transport of selected amino acids (alanine, phenylalanine, leucine, and lysine) were isotopically determined using a model based on arteriovenous blood samples and muscle biopsy. The intravenous amino acid infusion resulted in comparable increases in arterial amino acid concentrations at rest and after exercise, whereas leg blood flow was 64 +/- 5% greater after exercise than at rest. During hyperaminoacidemia, the increases in amino acid transport above basal were 30-100% greater after exercise than at rest. Increases in muscle protein synthesis were also greater after exercise than at rest (291 +/- 42% vs. 141 +/- 45%). Muscle protein breakdown was not significantly affected by hyperminoacidemia either at rest or after exercise. We conclude that the stimulatory effect of exogenous amino acids on muscle protein synthesis is enhanced by prior exercise, perhaps in part because of enhanced blood flow. Our results imply that protein intake immediately after exercise may be more anabolic than when ingested at some later time.