β-hydroxy-β-methylbutyrate (HMB) is a metabolite of the BCAA Leucine. Leucine has the greatest ability for initiating protein synthesis of the three BCAA's. Due to Leucine's ability to be catabolised within the muscle, there is the possibility that metabolites of this amino acid may be involved in mediating the effects of Leucine. Ultimately, HMB has the ability to facilitate the anabolic nature of Leucine, meaning greater strength, lean muscle mass and recovery gains. Recent studies have concluded that exognous HMB can increase muscle protein synthesis and reduce muscle protein breakdown. The branched-chain amino acid (BCAA) leucine acts as both a ‘trigger' for the initiation of protein synthesis, and as a substrate for newly synthesized protein. As a BCAA, leucine can be metabolized within skeletal muscle, leaving open the possibility that leucine metabolites might possess anabolic properties. One metabolite in particular, β-hydroxy-β-methylbutyrate (HMB), has shown positive effects on lean body mass and strength following exercise, and in disease-related muscle wasting, yet its impact on acute human muscle protein turnover is undefined. We report here that HMB stimulates muscle protein synthesis to a similar extent to leucine. HMB was also found to decrease muscle protein breakdown. Another study evaluated they effects of HMB supplementation on strength gains when combined with weight training. HMB + weight training resulted in an increase of strength gains by 4.8% per week, in comparison to only 3.4% per week with weight training alone. While the magnitude of the effect varies with training intensity and population studied, the overall effect was clear. HMB significantly increases strength gains when supplemented during resistance-exercise training. Further studies have also evaluated the effects of HMB on aerobic performance and health, of which both studies concluded HMB to have positive effects on both aerobic performance and objective measures of health and perception of well being.