Leucine Supplementation Has No Further Effect on Training-induced Muscle Adaptations

Leucine Supplementation Has No Further Effect on Training-induced Muscle Adaptations: Introduction

Several acute studies have suggested that leucine is a key amino acid to drive muscle protein synthesis. However, there are very few studies on the long-term effects of leucine supplementation on resistance training-induced gains in muscle mass and strength. We sought to determine the impact of 10 grams of leucine on muscle mass and strength in response to resistance training (RT) in healthy young men.

Methods

Twenty-five, resistance-trained men (27 ± 5 y; 78.4 ± 11.6 kg; 24.8 ± 3.0 kg/m2) consuming 1.8 ± 0.4 g protein·kg-1·d-1, were randomly assigned to receive 2 x 5 g·d-1 supplementation of either free leucine (LEU n=12) or alanine (PLA n= 13), while undergoing a supervised 12-week, twice- weekly lower-limb RT program. One-repetition maximum (leg-press 1RM) and muscle cross-sectional area (mCSA) of the vastus lateralis were determined before (PRE) and after (POST) the intervention. Additionally, three 24-hour dietary recalls were also performed at PRE and POST.

Results

Protein intake was roughly double that of the RDA in both groups and remained unchanged across time with no differences detected between groups. Similar increases were observed between groups in leg-press 1RM (LEU: 19.0 ± 9.4% and PLA: 21.0 ± 10.4%, p=0.31) and mCSA (LEU: 8.0 ± 5.6% and PLA: 8.4 ± 5.1%, p=0.77).

Conclusion

high-dose leucine supplementation did not enhance gains in muscle strength and mass after a 12-week resistance training program in young resistance-trained males consuming adequate amounts of dietary protein.

Corresponding author: Hamilton Roschel, PhD, Av. Prof. Mello Moraes, 65 - São Paulo, SP – Brazil - Zip Code: 05508-030, Phone: +55 11 3091-8783. E-mail: hars@usp.br

The authors acknowledge the support by Sao Paulo Research Foundation (FAPESP) (grant 2016/22083-3).

Conflict of interest. The authors have no conflict of interest to declare. The results of the present study do not constitute endorsement by ACSM. Finally, all authors herein declare that all the results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.

Accepted for Publication: 10 February 2020.

© 2020 American College of Sports Medicine