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Free leucine supplementation during an 8-week resistance training program does not increase muscle mass and strength in untrained young adult subjects


The purpose of this study was to examine the effects of free leucine supplementation on changes in skeletal muscle mass and strength during a resistance training (RT) program in previously untrained, young subjects. In a double-blind, randomized, placebo-controlled study, 20 healthy young (22 ± 2 years) participants were assigned to two groups: a placebo-supplement group (PLA, N = 10) or a leucine-supplement group (LEU, N = 10). Both groups underwent an 8-week hypertrophic RT program (2 days/week), consuming an equivalent amount of leucine (3.0 g/day in a single post-training dose) or placebo (cornstarch). Quadriceps muscle strength, cross-sectional area (CSA) of the vastus lateralis (VL), and rectus femoris (RF), as well as the habitual dietary intake were assessed before and after the 8-week intervention period. There was a similar improvement in muscle strength (Leg press, LEU: +33% vs. PLA: +37%; P > 0.05, and knee extension, LEU: +31% vs. PLA: 34%; P > 0.05) and CSA (VL, LEU: 8.9% vs. PLA: 9.6%; P > 0.05, and RF, LEU: +21.6% vs. PLA: + 16.4%; P > 0.05) in the both groups from pre- to post-training. In addition, there was no significant (P > 0.05) difference in daily dietary intake between the LEU and PLA groups before and after the intervention period. Free leucine supplementation (3.0 g/day post-training) does not increase muscle strength or CSA during RT in healthy young subjects consuming adequate dietary protein intake.

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Correspondence to Andreo Fernando Aguiar.

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No conflicts of interest, financial or otherwise, are declared by the author(s).

Human rights statement

This research involved human participants, who were carefully informed of the purpose, procedures, benefits, risks, and discomfort of the investigation, and signed an informed consent document approved by the Institutional Review Board of the University (Protocol No: 44487715.6.0000.0108–CAAE).

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Handling Editor: K. Niederreiter.

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Aguiar, A.F., Grala, A.P., da Silva, R.A. et al. Free leucine supplementation during an 8-week resistance training program does not increase muscle mass and strength in untrained young adult subjects. Amino Acids 49, 1255–1262 (2017).

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  • Nutritional supplementation
  • Hypertrophy
  • Cross-sectional area
  • Ergogenic
  • Skeletal muscle