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

Amino Acids. 2017 Jul;49(7):1255-1262. doi: 10.1007/s00726-017-2427-0. Epub 2017 Apr 25.


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.

Keywords: Cross-sectional area; Ergogenic; Hypertrophy; Nutritional supplementation; Skeletal muscle.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adolescent
  • Adult
  • Cross-Sectional Studies
  • Dietary Supplements*
  • Double-Blind Method
  • Female
  • Humans
  • Leucine / administration & dosage*
  • Male
  • Muscle, Skeletal / physiology*
  • Physical Endurance / drug effects*
  • Physical Fitness / physiology*
  • Time Factors


  • Leucine