High-dose HMB lifted aerobic markers but not strength

HMB has been studied almost entirely at a flat 3 g per day, a dose that ignores how much muscle a person actually carries. Scaling to fat-free mass is a plausible refinement, but nobody knew whether a much higher personalised dose would deliver anything beyond the modest effects already reported. There is also a persistent question about who benefits: supplements often look better in untrained people simply because they have more room to improve. This trial tested a high, body-composition-scaled liquid HMB dose in both trained and untrained men, with and without an added training stimulus.

Fifty-three trained and 37 untrained males completed a parallel, randomised, placebo-controlled, triple-blind trial spanning two consecutive 3-week periods. In the first, participants took either HMB free acid in liquid form at 90 mg per kg of fat-free mass per day or placebo while continuing their usual training or lifestyle. In the second, the same supplementation was combined with two weekly units of high-intensity functional training. Assessments at baseline and after each period covered body mass and composition, an incremental cycling test and maximal voluntary isometric contraction of the lower limb, analysed with a general linear model testing treatment, training status and baseline interactions.

Comparing the end of the training phase with baseline, trained men on HMB out-gained trained men on placebo across a wide spread of aerobic measures: VO2max, time to the anaerobic threshold, VO2 and power output and heart rate at that threshold, and time, VO2 and power output at the respiratory compensation point. Untrained men on HMB showed greater increases than placebo in only two indices, time and power output at the respiratory compensation point. Maximal voluntary isometric contraction did not change with treatment in either group. The clearest gains clustered around threshold and compensation-point measures rather than strength.

This extends HMB research beyond the standard 3 g protocol into personalised, fat-free-mass-scaled dosing, and it complicates the usual expectation that supplements do more for beginners. Here the trained group benefited on more indices, which the authors attribute to untrained participants likely needing more than two weekly training units and a longer intervention. The consistent null on isometric strength is notable given that supporting strength is one of HMB's marketing claims. Whether these threshold shifts persist, translate to real-world performance, or appear in women remains unanswered.

The pattern here points towards aerobic capacity and thresholds rather than strength, which is not where HMB is usually pitched. It also suggests that a supplement without an adequate training stimulus is unlikely to do much — the aerobic gains showed up in the phase that included high-intensity functional training. The dose used was scaled to fat-free mass and considerably higher than the amounts most products supply, so results here do not transfer to a standard serving. With three-week phases and men only, this is a reason for interest rather than confidence.