An Overview on Beta-hydroxy-beta-methylbutyrate (HMB) Supplementation in Skeletal Muscle Function and Sports Performance

Beta-hydroxy-beta-methylbutyrate (HMB) is a metabolite of the amino acid leucine. The first step in HMB metabolism is the reversible transamination of leucine to α-ketoisocaproate (KIC), which occurs mainly extrahepatically. Under normal conditions the majority of KIC is converted into isovaleryl-CoA, in which approximately 5% of leucine is metabolized into HMB. An individual weighing 70. kg produces about 0.2 to 0.4. g of HMB per day from dietary L-leucine. The vast majority of studies have employed 3. g/day of HMB, grounded in evidence that this dose produces better results than 1.5. g/day and is equivalent to 6. g/day. This metabolite has received attention due to its anti-catabolic properties, through inhibition of muscle proteolysis and enhancement of protein synthesis. The aims of HMB supplementation are to counteract catabolic conditions, as well to enhance skeletal muscle mass and strength in athletes, improving performance. Moreover, HMB has been shown to produce an important effect in reducing muscle damage induced by mechanical stimuli of skeletal muscle. HMB acts as precursor to the rate-limiting enzyme HMG-coenzyme A reductase in cholesterol synthesis, which can enhance sarcolemmal integrity. For these reasons, HMB supplementation has been adopted as an alternative by those practicing resistance exercise or weight training, by individuals under extreme muscular stress, by elderly individuals, and by patients with diseases associated with muscle-wasting syndromes, such as cachexia. This chapter discusses: aspects of HMB metabolism; supplementation protocols; effects on contractile function and energetic metabolism; and mechanisms of action, emphasizing molecular mechanisms described by recent findings. © 2013 Elsevier Inc. All rights reserved.