β-羥基-β-甲基丁酸鹽複合物（beta-hydroxy beta-methylbutyrate, HMB）為一種可由體內白胺酸（leucine）自行代謝生成的產物，亦可從食物中直接攝取，其作用於人體的機轉包含膽固醇合成假說、泛素蛋白酶途徑、哺乳動物雷帕黴素標靶蛋白途徑、核因子-κB途徑、有絲分裂活化蛋白質激酶／細胞外訊息調控蛋白激酶途徑及磷酸醇3激酶／Akt等六種。未受訓練者服用HMB可達到降低肌肉損傷指標及肌肉酸痛程度的效果，但此成效在有訓練經驗之運動員則較不顯著。目前補充HMB之理想劑量為一日3克，多量服用並無更高效益。針對肌肉損傷部份而言，補充HMB之效益可能因為肌肉損傷程度過高或訓練量過低，甚至服用時間太短導致效果不良；另外，以HMB配合肌酸或α-酮異己酸等增補劑，其效果並未加成甚至降低。未來探討HMB對肌肉損傷的影響，可進一步比較肌肉損傷嚴重程度、增補時間長短與服用HMB效益之相關性。

Derived from the amino acid leucine and its keto acid α-ketoisocaproate (KIC), β-hydroxy-β-methylbutyrate (HMB) has been well documented as an oral ergogenic supplement commonly used by athletes. HMB supplementation has been associated with significant increase in muscle mass and strength, and might reduce exercise-induce muscle soreness or damage. Previous studies indicate that supplementing 3g of HMB daily provides maximal benefits. Dialy consumption of HMB lower than the certain dosage provides lesser effects whereas higher doses have demonstrates no additional benefits. Previous reviews have emphasized six main pathways for HMB's mode of action: 1) enhancement of sarcolemml integrity via cytosolic cholesterol synthesis, 2) inhibits protein degradation via ubiquitine-proteasome pathway, 3) increase protein synthesis via mTOR pathway, 4) inhibits cell proliferation and differentiation through NF-κB pathway, 5) stimulates proliferation, differentiation and survival of myogenic cells via the MAPK/ERK, and 6) PI3K/Akt pathways. On the other hand, conflict results still remained between studies with different timing of supplement, duration of supplement and subjects. Several studies indicate that HMB supplement has been found to be more effective on untrained individuals. Combining HMB supplement with creatine or upstream metabolite α-ketoisocaproate does not provide further benefits. Further research is needed to determine the effects of HMB over longer periods of use or in other segments of training to clarifiy the efficacy of the supplement especially in highly trained athletes.

增補劑; 肌肉損傷; 延遲性肌肉酸痛; 作用機轉

ergogenic supplement; muscle damage; delayed-onset muscle soreness; mechanism