HMB supplementation combined with high-intensity functional exercise supports aerobic capacity but not strength in trained and untrained males: a randomized controlled trial.

BACKGROUND: β-hydroxy-β-methylbutyrate (HMB) supplementation may support aerobic capacity and isometric strength. Its utility has been studied mainly for 3 g HMB·day-1. Therefore, new and personalized HMB supplementation protocols should be verified. This parallel randomized placebo(PLA)-controlled triple-blind study was designed to evaluate the effects of liquid HMB free acid supplementation during customary training/lifestyle or combined with high-intensity functional training (HIFT) on aerobic fitness, physical capacity, and isometric strength indices following an incremental cycling test (ICT) in trained (TR) and untrained (UTR) males.

METHODS: Fifty-three TR (29.1 ± 7.7 years; body mass (BM): 84.8 ± 10.0 kg; FFM: 71.2 ± 8.9 kg) and 37 UTR participants (32.3 ± 7.6 years; BM: 90.1 ± 16.5 kg; FFM: 68.4 ± 10.3 kg) completed two 3-weeks periods, including: 1) supplementation period (SUP)-ingesting 90 mg·kgFFM -1·day-1 of either HMB or PLA and performing usual training (TR) or lifestyle (UTR), and 2) HMB/PLA ingestion combined with the additional HIFT stimuli (2 units per week; SUP + EX). TR_HMB, TR_PLA, UTR_HMB, UTR_PLA groups were analyzed. Testing visits were performed at baseline (T BAS ), and after the SUP (T SUP ) and the SUP + EX (T SUP+EX ). The following evaluations were performed: BM and body composition, ICT, and maximal voluntary isometric contraction (MVIC) of the lower limb. A general linear model was conducted to examine the main effects and interaction of treatment (supplementation) (HMB/PLA), training status (TS; TR/UTR), and baseline values (BAS) over repeated measurements (T BAS , T SUP , T SUP+EX ). The following interactions were tested: visit × treatment; visit × TS; visit × treatment × TS; and visit × treatment × TS × BAS. One-way ANOVA or Kruskal-Wallis ANOVA (non-normal distribution) were conducted to examine differences in the degree of absolute changes (ΔT SUP -T BAS , ΔT SUP+EX -T SUP , ΔT SUP+EX -T BAS ) in the measured indices between studied subgroups.

RESULTS: Increases (T SUP+EX -T BAS ) in VO2MAX (p = 0.024), time to the anaerobic threshold (AT; p < 0.001), VO2AT (p = 0.001), power output at the AT (p < 0.001), heart rate at the AT (p < 0.001), time to the respiratory compensation point (RCP; p < 0.001), VO2RCP (p < 0.001), power output at the RCP (p < 0.001) were higher in TR_HMB vs. TR_PLA. Simultaneously, in UTR, greater increases in TimeRCP (p = 0.001) and PowerRCP (p = 0.002) occurred with HMB supplementation compared to PLA. MVIC indices did not change due to the treatment.

CONCLUSIONS: Supplementation of high HMB dose combined with HIFT increases aerobic fitness and capacity, especially RCP and AT indices. HMB supplementation combined with HIFT evoked significant favorable changes in a greater number of the evaluated aerobic fitness and capacity indices in trained compared to untrained individuals. Thus, untrained individuals probably need greater exercise stimuli (>2 HIFT units per week) and a longer intervention period to obtained greater benefits. These findings suggest that incorporating liquid HMB supplementation at a dose of 90 mg·kgFFM -1·day-1 alongside HIFT is an effective strategy to enhance aerobic fitness and capacity in trained individuals, while further research including longer intervention periods and greater training stimuli is needed to determine the optimal supplementation protocol for untrained individuals.