The Twist: A Muscle Supplement That Moved the Cardio Needle
Beta-hydroxy-beta-methylbutyrate (HMB) has spent years in the "muscle and strength" aisle of the supplement world. A 2026 randomized trial in the Journal of the International Society of Sports Nutrition (Durkalec-Michalski et al.) suggests its more interesting payoff may be aerobic. In a triple-blind, placebo-controlled design, men who took a high, body-composition-adjusted dose of HMB while doing high-intensity functional training (HIFT) improved several cardiorespiratory markers more than placebo did. Maximal isometric leg strength did not change because of the supplement.
How the Study Was Run
The trial enrolled 90 men: 53 trained (average age about 29, fat-free mass about 71 kg) and 37 untrained (average age about 32, fat-free mass about 68 kg). Each participant went through two consecutive three-week blocks.
- Block 1 (SUP): HMB or placebo alongside usual training (trained group) or usual lifestyle (untrained group).
- Block 2 (SUP + EX): The same supplement plus two HIFT sessions per week.
The supplement was liquid HMB free acid dosed at 90 mg per kilogram of fat-free mass per day. Researchers tested at baseline and after each block. They used an incremental cycling test to capture VO2max, anaerobic threshold (AT), and respiratory compensation point (RCP), and a maximal voluntary isometric contraction (MVIC) test for lower-limb strength.
What Improved
In trained men, the HMB group beat placebo on the change from baseline to the end of the HIFT block in:
- VO2max (p = 0.024)
- Time to anaerobic threshold, VO2 at AT, power output at AT, and heart rate at AT
- Time to respiratory compensation point, VO2 at RCP, and power output at RCP
Most of these threshold-related differences carried p-values below 0.001. The VO2max result was the least emphatic, so the threshold markers are where the signal looks strongest.
These markers matter because they describe how much work you can sustain before fatigue accelerates. A higher power output at AT or RCP means you can hold a harder pace for longer, which is useful in mixed-modal sport, conditioning-heavy training blocks, and any event where you grind at a hard-but-sustainable effort.
What Did Not Improve
Isometric lower-limb strength showed no treatment effect. If you picked up HMB hoping for a bump in force production, this trial gives you no support. That fits a mixed history for HMB in strength outcomes, and it is a useful reminder that a supplement's marketing category and its measurable effect can diverge.
Trained vs. Untrained
The trained men benefited across a wider range of metrics. Untrained men saw greater gains from HMB only in time to RCP (p = 0.001) and power at RCP (p = 0.002). The authors suggest untrained people probably need more than two HIFT sessions per week and a longer intervention to see broader benefits. In other words, the supplement appears to work best when the training stimulus is already meaningful, and it may amplify adaptation rather than replace it.
The Dose Math
Most HMB research uses a flat 3 g per day. This trial scaled the dose to fat-free mass, so it is per-person rather than one-size-fits-all:
Daily dose (g) = 0.09 × fat-free mass (kg)
- 60 kg FFM: about 5.4 g/day
- 70 kg FFM: about 6.3 g/day
- 80 kg FFM: about 7.2 g/day
The average trained participant, at roughly 71 kg of fat-free mass, would have taken about 6.4 g daily. That is around double the conventional 3 g protocol. The abstract does not specify how the daily amount was divided, so don't assume a particular split. Note too that you need a reasonable estimate of fat-free mass, and consumer scales and calipers can be off by several kilograms, which shifts the number by a few hundred milligrams.
Who Might Care
The most plausible audience is trained hybrid athletes: CrossFit-style competitors, tactical athletes, and lifters who run conditioning-heavy blocks. For them, a shift in threshold power and time-to-threshold could be meaningful. Pure strength athletes looking for a max-strength edge have little reason to expect help from this data. Beginners should focus on getting a consistent training dose first.
Caveats Worth Keeping in Mind
- Short duration: Each block lasted only three weeks, so durability of the effect is unknown.
- Men only: The findings say nothing directly about women.
- Higher dose, less long-term data: The 3 g dose has far more research behind it, and the abstract does not address long-term use of roughly double that amount.
- Many outcomes: With numerous endpoints tested, the smaller p-values deserve more weight than the VO2max result, and replication would help.
- Single trial: One well-controlled study is a signal, not a settled answer.
Bottom Line
This trial reframes HMB as a possible aerobic-support supplement for people already training hard, not a strength booster. If you want to experiment, the evidence supports pairing a fat-free-mass-scaled dose with a real training stimulus and tracking something measurable, such as a sustained-effort test, rather than expecting changes on the bar. Treat it as promising rather than proven until longer and larger studies weigh in.
