Equivalent Hypertrophy and Strength Gains in HMB- or Leucine-supplemented Men

Ingestion of proteins with high leucine content during resistance training (RT) can augment hypertrophy. Some data suggest that a leucine metabolite, β-hydroxy, β-methylbutyrate (HMB), is substantially more anabolically efficacious than leucine. Purpose We aimed to test whether supplementation with HMB versus leucine, added to whey protein, would result in differential muscle hypertrophy and strength gains in young men performing resistance training. Methods Twenty-six resistance-trained men (23 ± 2 y) performed 12 wk of RT with 3 phases. Phase 1: 8 wk of periodized RT (3 training sessions/wk). Phase 2: 2 wk overreaching period (5 sessions/wk). Phase 3: 2 wk taper (3 sessions/wk). Participants were randomly assigned to twice daily ingestion of: whey protein (25 g) plus HMB (1.5 g) (Whey+HMB; n=13) or whey protein (25 g) plus leucine (1.5 g) (Whey+Leu; n=13). Skeletal muscle biopsies were performed before and after RT. Measures of fat and bone-free mass (FBFM), vastus lateralis (VL) muscle thickness and muscle cross-sectional area (CSA – both by ultrasound), muscle fiber CSA, and 1-repetition maximum (1-RM) strength tests were determined. Results We observed increases in FBFM, VL muscle thickness, muscle CSA and fiber type CSA and 1-RM strength with no differences between groups at any phase. We observed no differences between groups or time-by-group interactions in hormone concentrations at any phase of the RT program. Conclusion HMB added to whey did not result in greater increases in any measure of muscle mass, strength, or hormonal concentration compared to leucine added to whey. Our results show that HMB is no more effective in stimulating RT-induced hypertrophy and strength gains than leucine. Author for correspondence: Prof. Stuart Phillips, Ph.D. Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada, T: +1-905-525-9140 x24465, E: phillis@mcmaster.ca Submitted for publication May 2018. Accepted for publication July 2018. © 2018 American College of Sports Medicine

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