Leucine Supplementation Does Not Improve Muscle Recovery from Resistance Exercise in Young Adults: A Randomized, Double-Blinded, Crossover Study.

This study aimed to investigate the effects of free leucine supplementation on muscle recovery from resistance exercise (RE) in young adults. Fourteen untrained subjects (23.9 ± 3.6 years old) underwent RE sessions (leg press and hack squat: three sets of 8-12 reps at 70% 1RM) supplemented with leucine (LEU: two daily doses of 3g) or a placebo (PLA), separated by a seven-day washout period. Following each occasion, participants were evaluated in three subsequent days (24h, 48h, and 72h) for muscle recovery via a repetition-to-failure test. The following markers were assessed: repetition performance, perceived exertion, lactate, creatine kinase, muscle soreness (DOMS), testosterone, and cortisol. No significant difference was observed between LEU and PLA conditions ( > 0.05). Number of repetitions performed in the repetition-to-failure tests, perceived exertion, cortisol, and testosterone:cortisol ratio did not change over time ( > 0.05). Creatine kinase increased immediately after exercise, at 24h, and 48h, and was attenuated at 72h post-exercise, while testosterone, lactate, and DOMS increased at 24h post-exercise ( < 0.05) and remained elevated up to 72h. All outcomes were similar between LEU and PLA. Results indicate that a 6g daily dose of free leucine supplementation does not improve muscle recovery following lower-limb RE in untrained young adults.