β-羥基-β-甲基丁酸的生理作用與在運動表現的應用

Physiological effects of β-hydroxy-β-methylbutyrate and the applications on exercise performance

β-羥基-β-甲基丁酸（HMB）為白胺酸代謝產物，可活化mTOR路徑蛋白質合成作用，抑制泛素蛋白酶體之蛋白質分解作用，可能促進肌纖維肥大，緩減異化狀態之肌細胞凋亡與肌肉萎縮。健康成年人每日補充HMB3g，有助於阻力訓練後的肌肉增長與肌力提升。高齡者及患者補充HMB有助於緩減老化與病理因素所造成的肌肉流失現象。此外，HMB還可增加血液中類胰島素生長因子-1濃度，減少衛星細胞凋亡與促進肌細胞分化，可能提升肌肉再生能力。然而，補充HMB對運動員的肌力與肌肉量無顯著影響，可能是運動員未處於飢餓、氧化壓力等異化狀態，因此HMB所產生的抗異化效果有限。體重分級選手賽前減重，熱量攝取不足可能導致肌肉流失，補充HMB能否避免肌肉流失而維持運動表現，可進一步研究探討。β-hydroxy-β-methylbutyrate (HMB) is leucine metabolite. It has been suggested to promote protein synthesis via stimulating mTOR pathway and attenuate proteolysis via inhibiting ubiquitin-proteasome system. HMB may facilitate muscle hypertrophy and ameliorate muscle cell apoptosis and muscle atrophy in the catabolic states. It has been shown that HMB supplementation for 3 g/d could help to enhance muscle growth and strength after resistance training in healthy adults. HMB supplementation could help to alleviate muscle wasting induced by pathological conditions or aging in elderly and patients. In addition, HMB could also increase the concentrations of serum insulin-like growth factor-1. HMB may improve muscle regeneration capacity by reducing satellite cell apoptosis and promoting muscle cell differentiation. However, there is no significant effect of HMB supplementation on muscle strength and muscle mass in well-trained athletes. It is possible that these athletes are not in the catabolic states, e.g. starvation or oxidative stress. Therefore, the anti-catabolic effects of HMB may be limited. The athletes of weight category make weights before the competition. Energy deficit may contribute to muscle wasting in athletes. Further researches are warranted to investigate the effect of HMB supplementation to prevent muscle loss and maintain exercise performance in athletes during energy restriction period.