反覆性離心運動對神經適應與重複訓練效應之影響

Effect of a repeated bout of eccentric exercise on neural adaptation and repeated bout effect

緒論：進行第1回合最大離心運動 (maximal eccentric exercise, MAX1) 後會造成明顯的肌肉細微損傷，但是在肌肉損傷完全恢復之後，繼續讓相同肌群進行相同1回合運動訓練 (MAX2) 引起肌肉損傷的程度會明顯比MAX1來得小，此現象稱之為重複訓練效應 (repeated bout effect, RBE)。也有研究發現，單側肌群先進行MAX1並間隔2週休息後，改換成對側肌群進行MAX2時亦可產生RBE (稱為：RBE交叉轉移效果)，但若在2回合運動訓練之間休息6週，即無法產生RBE交叉轉移效果。所以，目前還不清楚MAX1與MAX2之間，間隔休息大於2週或小於6週的RBE交叉轉移效果為何。因此，本研究目的，初步針對單側肘屈肌群 (elbow flexors, EF) 進行MAX1後，間隔休息23天再換成對側EF進行相同一回合離心運動 (MAX2) 時，是否能有效產生RBE交叉轉移效果，並進一步探討此RBE交叉轉移效果是否藉由神經適應所產生之假設。方法：16位大學健康成年男性分為實驗組 (EXP) 與控制組 (CON，每組8人)，EXP以平衡次序 (左右手EF各分一半) 先讓單側EF進行30次MAX1 (30°/s) 後23天，改由對側EF進行MAX2；CON以同側非慣用手EF，在進行MAX1-2之間間隔休息23天。MAX1-2記錄力矩峰值 (peak torque, PT)、表層肌電訊號 [均方根值 (root mean square, RMS)、平均數功率頻率 (mean power frequency, MPF)]。肌肉損傷指標計有：肌肉酸痛 (muscle soreness, SOR)、肘關節放鬆角度 (relaxed elbow joint angle, RANG)及最大等長肌力 (maximal voluntary isometric contraction strength, MVC) 在MAX1-2前、後第0-3天各測1次。結果：兩組的肌肉損傷指標在MAX1 (如MVC最大下降率：-42%) 與MAX2後均明顯改變 (-33%; p < .05)，MAX2後恢復速度 (如SOR峰值：16mm、RANG：-3°) 優於MAX1 (SOR峰值：33mm、RANG：-6°；p < .05)，但兩組之間分別在MAX1與MAX2後的恢復速度無差異 (p > .05)。兩組僅在MAX2的MPF明顯低於MAX1 (-14%, p < .05)。結論：單側EF進行MAX1後，繼續改用對側EF進行MAX2時，可有效產生RBE；此RBE可能是藉由招募較多第1型肌纖維參與對側MAX2，進而產生RBE交叉轉移效果與降低肌肉損傷之效果。

Introduction: Cross-transfer is a phenomenon in which training of the muscles in one limb increases the strength of those same muscles in the contralateral limb. An initial bout of maximal eccentric exercise (MAX1) results in significant muscle damage, but repeating the same maximal eccentric exercise (MAX2) following full recovery from MAX1 (>2 weeks later) significantly attenuates changes in muscle damage markers. This adaptation is referred to as the repeated bout effect (RBE). Previous studies have reported that the RBE can also be conferred by MAX1 performed with a certain muscle group of one limb against muscle damage induced by MAX2 performed 2 weeks later with the same muscle group of the opposite limb. This is called cross-transfer RBE (CF-RBE). However, no CF-RBE was observed if MAX1 and MAX2 were performed 6 weeks apart. It is currently not known whether the CF-RBE will be observed when MAX2 is performed more than 2 weeks, but less than 6 weeks after MAX1. Therefore, the purpose of the present study was to investigate the hypothesis that: 1) the CF-RBE conferred by MAX1 performed with the elbow flexors (EF) of one arm would attenuate muscle damage induced by MAX2 performed 23 days later with the EF of the opposite arm; and 2) the CF-RBE would be mediated by neural adaptations. Methods: Sixteen healthy young men were assigned to either an experimental (EXP) or control group (CON, n = 8/group). EXP subjects performed MAX1 (30°/s) using the EF of one arm (using a counterbalanced method), followed 23 days later by MAX2 using the contralateral EF. CON subjects performed MAX1-2 using the same non-dominant EF, also separated by 23 days. Peak torque (PT) and surface electromyography [root-mean-square (RMS), mean power frequency (MPF)] were recorded during MAX1-2. Muscle soreness (SOR), relaxed elbow joint angle (RANG) and maximal voluntary isometric contraction strength (MVC) were measured before, immediately after, and 1-3 days after each exercise. Results: All dependent variables showed significant changes (p < .05) following MAX1 (e. g. MVC lowest loss: -42%) and MAX2 (-33%) for the EXP and CON groups. Changes in all dependent variables following MAX2 were significantly smaller (e.g. peak-SOR: 16 mm; RANG: -3°) than following MAX1 (peak-SOR: 33 mm; RANG: -6°; p < .05), without significant difference in all variables between the EXP and CON groups (p > .05). Only MPF showed a significant decrease (14%, p > .05) during MAX2 compared with MAX1. Conclusion: MAX1 performed with the EF of one arm could induce CF-RBE, and effectively attenuate muscle damage induced by MAX2 performed with the EF of the opposite arm. This effect is likely mediated by recruiting an increasing number of type I muscle fibers.