PURPOSE: In vitro, the amino acid leucine has been able to reduce proteolysis and be a potent stimulus for protein synthesis. The purpose of this study was to determine the effect of leucine supplementation on indices of muscle damage and muscular function following eccentric-based resistance exercise. METHODS: Twenty-seven untrained individuals (Height: 178.62 +/- 5.54 cm; Mass: 77.71 +/- 13.46 kg) were randomly divided into 3 groups; leucine, placebo and control. The leucine and placebo groups performed 100 depth jumps from 60 cm and 6 sets of 10 repetitions of eccentric-only leg presses. Either leucine (250 mg/kg bm) or placebo was ingested at 3 time points during exercise and each recovery day following exercise. Each group's level of muscle damage was determined via serum levels of creatine kinase and myoglobin at pre-exercise (PRE) and 24, 48, 72 and 96 hours post-exercise. Creatine kinase was assessed using basic spectophotometric techniques and myoglobin was assessed using an ELISA. Muscle function was determined by peak force (PF) during an isometric squat and jump height (JH) and peak concentric force (PCF) during both a static jump (SJ) and countermovement jump (CMJ) at PRE and 24h, 48h, 72h and 96h post-exercise. Data was analyzed using a general linear model with repeated measures and Bonferroni post hoc tests. RESULTS: Creatine kinase was significantly elevated from PRE (354.8 +/- 317.5 U/L) for the leucine group at 24h (713.4 +/- 473.0 U/L) and significantly elevated from PRE (185.9 +/- 117.7 U/L) for the placebo group at 72h (501.7 +/- 434.3 U/L) and 96h (455.6 +/- 326.0 U/L). Myoglobin was significantly elevated from PRE (24.03 +/- 15.4 ng/ml) for the placebo group at 24h (66.3 +/- 59.6 ng/ml) and 96h (52.9 +/- 41.3 ng/ml). PF for the isometric squat significantly decreased across all time points for placebo group and 24h, 48h, and 72h for the leucine group. SJ JH significantly decreased from PRE (0.42 +/- 0.05 m) for the placebo group at 24h (0.38 +/- 0.04 m), 48h (0.38 +/- 0.06 m) and 72h (0.39 +/- 0.04 m). CMJ JH significantly decreased from PRE (0.46 +/- 0.03 m) for the leucine group at 48h (0.42 +/- 0.04 m), 72h (0.43 +/- 0.03 m) and 96h (0.39 +/- 0.14 m) and also from PRE (0.48 +/- 0.05 m) for the placebo group at 24h (0.44 +/- 0.08 m), 48h (0.43 +/- 0.07 m) and 72h (0.43 +/- 0.06 m). SJ PCF significantly increased from PRE (1652.1 +/- 226.0 N) for the leucine group at 48h (1728.9 +/- 264.8 N), 72h (1725.8 +/- 279.5 N) and 96h (1730.0 +/- 270.0 N) and was significantly higher compared to the placebo group at 24h and 48h. CMJ PCF significantly increased from PRE (1673.6 +/- 308.7 N) for the placebo group at 48h (1760.6 +/- 399.5 N). CONCLUSIONS: Leucine supplementation does not appear to be a viable choice for reducing immediate muscle damage following eccentric exercise; however leucine may facilitate the recovery process. Leucine may need further examination, as it was unable to shown a between group difference compared to placebo but did minimize the change in muscle damage markers compared to PRE. Leucine supplementation did not attenuate the initial decrement in PF during an isometric squat but did return PF back to baseline by the 96 hour time point. For contractions that are not accompanied by a stretch-shorten cycle, leucine supplementation minimized the decrement in muscle function and maintained PF output when compared to a placebo. Practical Applications: Supplementing with leucine by itself may not completely reduce the levels of muscle damage that follow high-intensity resistance training, but may help maintain force generating capabilities. Therefore, increasing leucine consumption, in concurrence with other nutritional recovery protocols, may help maintain muscle function during contractions that are not preceded by a stretch-shorten cycle.
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