In healthy men aged 67 to 69 who are doing progressive strength training for six weeks, taking 3 grams of HMB-free acid daily might be linked to a small increase in thigh muscle mass compared to a placebo, but this effect was not seen consistently in other muscle measurements or function tests.

We analyzed one assertion on HMB-free acid and thigh muscle mass in older men doing resistance training, and it supports the idea that taking 3 grams daily for six weeks might be linked to a small increase in thigh muscle mass among healthy men aged 67 to 69, compared to a placebo [1]. This effect was not seen in other muscle measurements or in tests of strength or function. What we’ve found so far is limited to just this single study, and while it points to a possible small benefit in thigh muscle mass, it does not show consistent changes elsewhere in the body or improvements in how the muscles work. There are no studies in our review that contradict this finding, but there are also no other studies to confirm or expand on it. The evidence we’ve reviewed leans toward a minor, localized effect — but we cannot say whether this change is meaningful in daily life, or if it would last beyond six weeks. HMB-free acid is a compound related to the amino acid leucine, which the body uses to build muscle. In this case, it was given as a supplement alongside regular strength training. The study focused only on men in their late 60s, so we don’t know if the same result would appear in women, younger people, or those with health conditions. For now, if you’re an older man doing resistance training and considering HMB-free acid, this one study suggests it might help a little with thigh muscle size — but not necessarily with strength or overall function. More research is needed to understand if this effect is real, lasting, or useful in the long term.