23 – HMB Supplementation: Clinical and Performance-Related Effects and Mechanisms of Action

β-Hydroxy-β-methylbutyrate (HMB) is a leucine-derived compound with anabolic and anticatabolic properties that may improve both clinical and performance outcomes. Clinically, HMB supplementation has been shown to decrease muscle proteolysis and spare muscle mass during catabolic states associated with muscle wasting syndromes. In resistance training studies, HMB may promote enhanced gains in muscle mass and strength. When evaluating the potential effects of HMB, dosage, form (calcium and the free acid form), and subject status (atrophic or anabolic states) must be taken into consideration. This chapter aims to describe general scientific evidence on HMB supplementation with regard to clinical outcomes, as well as their effects associated with resistance training and other sports. Possible mechanisms of action are also discussed in detail, based on the physiological, biochemical, and cellular/molecular literature.