Is hydroxy-methylbutyrate (HMB) the new creatine?
Recently an ergogenic aid called β-hydroxy- β-methylbutyrate or HMB, has been commercially marketed as the new performance enhancer for weight lifting and sprint activities. HMB is metabolite of the amino acid leucine and it is naturally synthesized in our bodies (i.e., 0.2 to 0.4 g of HMB/day). Proponents of HMB claim that supra-endogenous quantities of HMB (i.e., 3 to 6 g of HMB/day) reduced exercise induce muscle proteolysis, thereby producing positive effects on strength and body composition which include increased fat-free mass and reduction in fat mass, increase in leg extension, bench press, and total body strength. Empirical evidence on the effects of HMB on athletic performance remains limited, however. When combined with intensive resistance training, HMB has been shown to increase total body strength and fat-free mass in groups of untrained individuals (Nissen, et al., 1996; Slater & Jenkins, 2000). The mechanism of action of HMB remains unknown, however.
Effects of HMB on athletic performance
Oral supplementation of β-hydroxy- β-methylbutyrate (HMB) has been purported as having performance enhancing benefits (Knitter, et al., 2000; Nissen, et al., 1996; Nissen, et al., 2000; Nissen & Sharp, 2002; Slater & Jenkins, 2000). The proposed ergogenic benefits of HMB supplementation include a reduction in exercise induced proteolysis (Nissen, et al., 1996; Slater & Jenkins, 2000) and body fat as well as increases in total body strength and fat-free mass in groups of untrained individuals (Nissen, et al., 1996). All of the demonstrated effects of HMB have emerged in combination with intensive resistance training.
The mechanisms by which HMB impact athletic performance remain elusive. Nissen et al., 1996 have proposed that HMB may serve as a structural component within cell tissues and membranes by covalently binding to cell membrane components and increasing their structural integrity. In support of this hypothesis, muscle proteolytic-indicating enzymes have been shown to be significantly lower in HMB-supplemented subjects when compared placebo-supplemented subjects (Knitter, et al., 2000; Nissen, et al., 1996). However, the exact mechanisms by which HMB inhibits or attenuates muscle proteolysis remain unidentified. HMB positive anabolic effects on muscle strength and muscle mass seem to be due to an overall reduced catabolic state following intense resistance exercise training instead of a direct effect on muscle anabolism.
Research on the effects of HMB on aerobic performance to endurance training is scant. In one such study, Knitter et al., 2000 evaluated the 20-km running performance of a group of experienced male and female distance runners. The results showed that after six weeks of HMB supplementation in combination with endurance training HMB-supplemented subjects exhibited significantly lower plasma concentrations of both creatine phosphokinase (CK) and lactate dehydrogenase (LDH) than the placebo-supplemented group. Knitter et al. concluded that HMB supplementation inhibits endurance exercise-induced muscle damage. Similarly, Vukovich & Dreifort, 2001 have examined effects of two weeks of HMB supplementation on the Onset of Blood Lactate Accumulation (OBLA) and VO2 peak in a group of experienced cyclists. HMB supplementation significantly increased the time to OBLA in the HMB-supplemented group when compared to the placebo-supplemented group. VO2 peak was unaffected by HMB supplementation.
The effects of HMB on anaerobic capacity and intermittent performance have not received any research consideration. Both anaerobic and intermittent activities have been shown to induce significant muscle damage (Mohr & Bangsbo, 2001). Consequently, based on the proposed mechanism of action of HMB, athletes of sports which involve large anaerobic or intermittent performance components may benefit from HMB supplementation.
Conclusions
To date HMB and creatine remain the only two dietary supplements that have been consistently shown to increase lean body mass and improve strength gains when combined with a resistance training program (Nissen & Sharp, 2002). Nevertheless, HMB effects on aerobic, anaerobic, and intermittent performances as well as its mechanism(s) of action remain to be determined.
References
Knitter, A. E., Panton, L., Rathmacher, J. A., Petersen, A., and Sharp, R. (2000).
Effects of β-hydroxy- β-methylbutyrate on muscle damage after a prolonged run. J. Appl. Physiol., 89, 1340-1344.
Mohr, M., & Bangsbo, J. (2001). Development of fatigue towards the end of a high level soccer match. Med. Sci. Sports Exerc. 33, 215.
Nissen, S. L., Sharp, R., Ray, M., Rathmacher, A., Rice, D., Fulller, J.C., Connelly, A.S., & Abumrad, N. (1996). Effect of leucine metabolite β-hydroxy- β-methylbutyrate on muscle metabolism during resistance-exercise training. J. Appl. Physiol., 81 (5), 2095-2104.
Nissen, S. L., Sharp, R. L., Panton, L., Vukovich, M., Trappe, S., and Fuller, J. C. (2000). β-hydroxy- β-methylbutyrate (HMB) supplementation in humans is safe and may decrease cardiovascular risk factors. J. Nutr., 130, 1937-1945.
Nissen, S. L., & Sharp, R. L. (2002). Effect of dietary supplements on lean mass and strength gains with resistance exercise: a meta-analysis. J. Appl. Physiol. 94, 651-659.
Slater, G. J., & Jenkins, D. (2000). β-hydroxy- β-methylbutyrate (HMB) supplementation and the promotion of muscle growth and strength. Sports Med. 30 (2), 106-116.
Vukovich, M. D., & Dreifort, D. (2001). Effect of β-hydroxy- β-methylbutyrate on the onset of blood lactate accumulation and VO2 peak in endurance-trained cyclists. J. Strength Cond. Res., 15 (4), 491-497.