Net Protein Balance after Load Carriage Exercise is Enhanced by Amino Acid Supplementation

Abstract

Essential amino acid (EAA) supplementation during conventional endurance (CE) exercise attenuates post-exercise protein breakdown (PB) and enhances net protein balance (NET). Whether consuming EAA during load carriage endurance (LC) exercise confers the same anabolic effect is not clear, as the metabolic and mechanical strain of LC could upregulate protein turnover and branched-chain amino acid oxidation (OX). This study examined whole-body protein turnover during recovery from LC and CE with and without EAA supplementation using the reciprocal-pool model. Forty adults (mean ± SD, 22 ± 4 y, 80 ± 10 kg, 4.0 ± 0.5 L•min-1) were randomly assigned to perform a 90 min LC (24 ± 3 kg load), or metabolically-matched (2.2 ± 0.1 L•m-1), CE (cycle ergometry) exercise bout, during which EAA (10 g EAA, 37% leucine) or nonnutritive control (CON) drinks were consumed. Post-exercise PB was lower and OX was higher for EAA (53 ± 13 and 23 ± 4 µmol·kg-1·h-1) than CON (102 ± 13 and 10 ± 1 µmol·kg-1·h-1), irrespective of exercise mode (P < 0.05). Similarly, NET was not influenced by exercise mode, but was higher (P < 0.05) for EAA (49 ± 8 µmol·kg-1·h-1) than CON (-3 ± 1 µmol·kg-1·h-1). No other differences in protein turnover were observed. These data confirm the protein-sparing effect of EAA supplementation during endurance exercise, and suggest that if the metabolic demands are equivalent, whole-body protein turnover responses to weighted and non-weight bearing endurance exercise are the same. Supported by US Army Medical Research and Material Command and US Army Combat Feeding Directorate.