HMB (β-hydroxy-β-methylbutyrate)
Evidence: limited
An emerging aid, not a proven one. The endurance evidence is genuinely split between meta-analyses; the steadier signal is faster recovery from muscle-damaging sessions. No water-weight penalty, unlike creatine.
Not medical advice
This is a general knowledge base, not medical or dietary advice. If you are injured, unwell or weighing up a supplement or a change to your diet, speak to a doctor, physiotherapist or registered dietitian who knows your situation.
HMB is a metabolite of the amino acid leucine, sold on claims that it curbs muscle breakdown, speeds recovery and lifts endurance. The Australian Institute of Sport (AIS) places it in Group B, its emerging-evidence tier for supplements that warrant further research rather than a firm recommendation. That is the honest headline: more promising than the supplements that flatly fail, short of the proven ones.
The endurance case rests on two meta-analyses that disagree. Fernández-Landa et al. 2024 pooled 11 RCTs (n = 279) of 3 g per day for 2 to 12 weeks and found a significant improvement in both endurance performance and VO₂max (SMD ≈ 0.58), though the sample was small and mostly recreationally active rather than trained runners. A broader 2025 network meta-analysis of 30 RCTs (693 athletes) found no significant effect on VO₂max (SMD 0.28, 95% CI −0.05 to 0.61) or on endurance performance (SMD 0.29, 95% CI −0.44 to 1.03), and reported that no supplement it examined reliably raised VO₂max (Deng et al. 2025). The detail that reconciles them is training load: HMB’s benefit looks largest under heavy, muscle-damaging training and hardest to detect in already well-trained athletes under a normal load (Deng et al. 2025).
The steadier signal is recovery from muscle damage. A review of that literature found HMB consistently lowered creatine kinase and lactate dehydrogenase, the blood markers of muscle-membrane damage, and reduced soreness (Kim & Kim 2022). Two of its findings bear directly on running: smaller rises in those markers after a 20 km run, and faster recovery of muscle function after downhill running (Kim & Kim 2022). The ISSN position stand reports the same 20 km result and rates recovery as one of HMB’s better-supported effects (Rathmacher et al. 2024). Not every trial agrees, and the mechanism is incompletely understood.
For the gym work that supports running, the picture is modest. The 2025 network meta-analysis found HMB improved anaerobic peak power (SMD 0.60) and mean power (SMD 0.45) but ranked it behind protein, creatine and beta-alanine on both (Deng et al. 2025). Its effect on body composition and strength from resistance training is smaller than that of leucine itself or a good protein intake (Rathmacher et al. 2024), and it adds nothing when taken alongside creatine (Kim & Kim 2022). So it is not a first-choice training aid.
The standard dose is 3 g per day. The ISSN stand reports no adverse effects at up to 6 g per day for eight weeks or at 3 g per day for a year, with no impairment of glucose metabolism or insulin sensitivity (Rathmacher et al. 2024).
The reasonable reading: not core kit, but a defensible experiment for a runner in a heavy training block who wants to blunt muscle damage and recover between hard sessions, with the endurance payoff unproven and dependent on which meta-analysis holds up. Its one clear edge over creatine for weight-bearing runners is that it carries no water-weight gain.