Leucine supplementation during endurance exercise enhances post‐exercise muscle protein synthesis

Abstract

The benefit of leucine-enriched amino acid supplementation on muscle protein synthesis following resistance exercise has been well established. However, the effects after sustained aerobic-type exercise are not well described and may differ, given that muscle contractile forces generated are normally lower. This study examined how essential amino acid (EAA) supplementation, of varying leucine content, affected mixed muscle protein synthesis (MPS), whole body leucine oxidation (Ox), and non-oxidative leucine disposal (NOLD) following sustained aerobic-type exercise. Ten adults completed two separate 60 min bouts of cycle ergometry (60% VO2peak), during which isonitrogenous (10 g EAA) drinks containing leucine-enriched EAA (L-EAA; 34% leucine) or EAA (18% leucine) were consumed. MPS and leucine kinetics were determined using primed, continuous infusions of [2H5]-phenylalanine and [13C]-leucine. Plasma leucine levels were higher (P < 0.05) post-exercise for L-EAA relative to EAA for up to 3.5 h into recovery. Post-exercise MPS was higher (P < 0.05) for L-EAA compared to EAA (0.078 ± 0.01 vs. 0.056 ± 0.01 %/h). Post-exercise leucine Ox was 65% higher (P < 0.05) and NOLD was 19% lower (P < 0.05) for L-EAA than for EAA. Leucine supplementation during sustained steady-state exercise appears to have similar beneficial effects on MPS as during resistance-type exercise.