Beta-hydroxy-beta-methylbutyrate (HMB) has been used extensively as a dietary supplement for athletes and physically active people. HMB is a leucine metabolite, which is one of three branched chain amino acids. HMB plays multiple roles in the human body of which most important ones include protein metabolism, insulin activity and skeletal muscle hypertrophy. The ergogenic effects of HMB supplementation are related to the enhancement of sarcolemma integrity, inhibition of protein degradation (ubiquitin pathway), decreased cell apoptosis, increased protein synthesis (mTOR pathway), stimulation of the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis and enhancement of muscle stem cells proliferation and differentiation. HMB supplementation has been carried out with various groups of athletes. In endurance and martial arts athletes, HMB supplementation revealed positive effects on specific aerobic capacity variables. Positive results were also disclosed in resistance trained athletes, where changes in strength, body fat and muscle mass as well as anaerobic performance and power output were observed. The purpose of this review was to present the main mechanisms of HMB action, especially related to muscle protein synthesis and degradation, and ergogenic effects on different types of sports and physical activities.

Background: The purpose of this study was to examine the acute effect of a caffeine-based multi-ingredient supplement (MS) on the reactive agility and jump performance in recreational handball male players. Methods: A randomized, double-blind, crossover study involved twenty-four male handball players. All participants were tested under three conditions: placebo, caffeine, or MS ingestion 45 minutes before exercise tests. Participants performed a reactive agility test (Y-test: 1-1-2 test) and countermovement jump (CMJ).Results: None of the supplements improved countermovement jump height. The time needed to complete the 1-1-2 test was significantly shorter in MS condition compared to placebo. The differences in agility between PL vs. caffeine and MS vs. caffeine conditions were not statistically significant.Conclusions: The results of this study indicate that the caffeine-based multi-ingredient performance was effective in improvement in reactive agility but not in jump height in recreational handball male players. A similar effect was not observed with caffeine ingestion alone. Further comparative studies (MS ingestion vs. only caffeine ingestion) and MS with different compositions are needed.