Journal Title (Medline/Pubmed accepted abbreviation): Eur J Appl Physiol
Page number: 2261-2269
doi : 10.1007/s00421-011-1855-x
Background: β-hydroxy β-methylbutyric acid (HMB) is a bioactive metabolite of the branch chain amino acid leucine that promotes strength gain and increase in fat-free mass (FFM) in adults during resistance training. In conjunction with ketoisocaproate, another leucine metabolite, HMB may inhibit protein degradation through stabilization of muscle cell membrane and inhibition of the ubiquitin-to-proteosome system. In addition, HMB directly contributes to protein synthesis, possibly through upregulation of insulin-like growth factor-1 (IGF-1) and mammalian target of rapamycin (mTOR) signaling in skeletal muscle. Despite these observations, the potential benefit of HMB supplementation during strength training remains unconfirmed.
Hypothesis/purpose of study: HMB supplementation will increase FFM, muscle strength, anaerobic and aerobic capacity; will increase anabolic and reduce catabolic hormonal response; and will decrease inflammatory response to resistance training.
Subjects: Twenty-nine (15 males, 14 females) healthy, elite-level Israeli junior volleyball players (age, 13.5 to 18 y; Tanner stage [pubic hair], 4 to 5) participated in the study. Mean demographic and anthropometric subject characteristics (control and HMB, respectively) were: age, 16.2 and 16.1 y; height, 181.9 and 185.0 cm; weight, 69.9 and 72.3 kg; body mass index, 21.1 and 21.0 kg/m2.
Experimental design: Randomized, double-blind, placebo-controlled
Treatments Protocol: The study was performed during the first 7 weeks of the Israeli volleyball season because previous research suggests a greater response to HMB in untrained individuals. Participants from both HMB- and placebo-treated groups trained (18 to 22 hr/wk), ate, and lived together for the duration of the study. HMB (3 g daily) or placebo was administered by pill every day during practice in front of the coaches. Training consisted of tactical and technical drills emphasizing volleyball skills and team strategies (~ 20% of training), power and speed drills (~25% of training), interval sessions (~25% of training), endurance-type training (ie, long-distance cross-country running; 15%), and resistance training (primarily circuit training with free weights at 65% to 75% of maximal 1 repetition [1-RM]; 15%). Fitness assessments before and after the 7-week training included power (vertical jump test), strength (upper and lower limb strength using 6-RM and isokinetic force), anaerobic power (Wingate anaerobic test), aerobic power test (20-min shuttle run), nutritional assessments (2-day food record), habitual activity assessment, blood sampling and analysis (growth hormone [GH], IGF-1, IGF-1 binding protein 3, lactate, cortisol, testosterone, inflammatory mediators, interleukin [IL]-6, and IL-1 receptor antagonist [IL-1ra]).
Athletes often begin utilizing nutritional supplements during adolescence, despite an absence of scientific evidence for efficacy and safety of many supplements in this population. Because of the rapid growth that occurs during adolescence, a solid understanding of the effects of supplements such as HMB on physiology, growth, and increased muscle mass is needed. HMB supplementation resulted in greater increases in muscle mass, muscle strength, and anaerobic fitness than placebo. HMB did not demonstrate a detrimental effect on aerobic capacity, and its use was not associated with changes in expression of hormonal or inflammatory mediators. These results suggest that HMB supplementation may improve athletic performance and strength in elite adolescent volleyball players early at the start of the training season.