HMB, a metabolite of the essential amino acid leucine, is a dietary supplement used to enhance gains in strength and lean body mass associated with resistance training. Unlike anabolic (muscle building) hormones that induce muscle hypertrophy by increasing muscle protein synthesis, HMB is claimed to influence strength and lean body mass by acting as an anticatabolic (decrease muscle breakdown) agent, minimizing protein breakdown and damage to cells that may occur with intense exercise.
Research on HMB has recently tested this hypothesis, under the assumption that it may be the active compound associated with the anticatabolic effects of leucine and its metabolites. While much of the available literature is preliminary, there is support for the claims made regarding HMB supplementation- at least in young, previously untrained individuals. A mechanism by which this may occur is unknown, but research undertaken to date suggests there may be a reduction in skeletal muscle damage. The response of resistance trained and older individuals to HMB administration is less clear.