Leucine-enriched essential amino acids (LEAA) can acutely enhance post-exercise muscle protein synthesis and may facilitate muscle damage recovery, although the relationship between these outcomes during the prolonged post-exercise recovery period is unclear. PURPOSE: We aimed to determine the effect of LEAA on ‘free-living’ rates of myofibrillar protein synthesis (MyoPS) and its relationship to markers of muscle damage after an unaccustomed bout of resistance exercise (RE) in recreationally-active men. METHODS: Twenty healthy males (24.1 ± 4.3 yrs) consuming a controlled diet (1.2g/kg/day of protein) were randomized to consume 4.0g of LEAA (containing 1.6g leucine) or isocaloric placebo (PLA) thrice daily for four days following an acute bout of lower-body RE (5x12 repetitions at 75% maximum of leg press and knee extension). MyoPS at rest and over 96h of recovery was measured by D₂O (150ml, 70% APE) with body water enrichment as the precursor. Total muscle torque (sum of isometric and 60 and 270°/s isokinetic torques; SUM) of the knee extensors, thigh muscle soreness (SOR), Z-band streaming, and muscle heat shock protein (HSP) 25 and 70 expression were measured at rest and during recovery. RESULTS: MyoPS increased ~72% after RE (P < 0.01) with no differences between groups (P > 0.05). By 48h, SUM decreased ~21% and SOR increased (all P < 0.01) with both variables generally returning to baseline by 96h. Compared to PLA, LEAA consumption significantly attenuated the decrease in SUM (P < 0.05) and had small-to-moderate effects on decreasing SOR. HSP25 increased ~16% post-RE (P < 0.05) with no difference between groups (P > 0.05). Consistent with a trend toward increased Z-band streaming in PLA (P = 0.07), HSP70 expression increased ~32% more (P < 0.05) during recovery in PLA as compared to LEAA. SUM correlated with SOR (r = -0.64, P < 0.05) whereas there were no correlations between MyoPS and any other outcomes (P > 0.05). CONCLUSION: Daily consumption of LEAA mitigates muscle strength loss and may moderately alleviate muscle
damage during recovery from an unaccustomed bout of resistance exercise in recreationally-active men, but this does not appear to be related to the extent of myofibrillar protein synthesis.
Supported by Ajinomoto Co. Inc.