優秀女子排球選手下肢負重增強式動作的神經力學分析
摘要
負重增強式訓練（Plyometric Weight Training）是一種結合重量訓練可增進最大肌力及增強式訓練可提升動作速度的爆發力訓練法。本研究旨在探討不同負荷下進行負重下蹲反彈跳（loaded counter-movement jump，簡稱LCMJ，典型的下肢負重增強式動作）訓練對爆發力、神經肌肉的徵召活化效果、運動單位的激發頻率…等神經力學參數的影響。
本研究以大專排球聯賽特優級優秀女子排球選手12人為受試對象(年齡：19.9±1.1歲，身高： 171.8±6.8公分，體重：64.83±6.03公斤)。本實驗先以Quattro Jump單軸測力板測量受試者下肢蹲舉的最大等長肌力，作為個別負荷強度的訂定依據，再隨機選擇不同負荷（最大等長肌力的0%, 10%, 20%, 30%, 40%），分別進行有、無反向動作的LCMJ與負重屈膝蹲跳（loaded squat jump，簡稱LSJ）動作測試，並利用測力板、位移計與Biovision肌電系統，同步收集受試者在史密斯訓練器進行LCMJ與LSJ動作的力量、位移與肌電訊號，再以 DasyLab與Acqknowledge軟體擷取相關的神經力學參數。肌電資料的收集包括股直肌、股外側肌、比目魚肌、腓外側肌、股二頭肌和脛骨前肌，肌電資料的分析是以標準化均方根肌電振幅（root mean square of EMG, 簡稱EMGrms）來評估運動單位的徵召量，而以中位數頻率（median frequency, 簡稱MDF）來評估運動單位的激發頻率與類型。統計方法是以相依樣本二因子變異數分析來考驗不同負荷與不同負重蹲跳動作對神經力學參數的差異。
研究結果顯示：負重增強式動作在力量與爆發力的輸出上具有力學上的優勢，LCMJ顯著優於LSJ，且隨負荷的增加而增加；但在神經支配因素的優勢上則受負荷重量與動作速度的雙重影響而抵銷其肌肉活化程度，這導致LCMJ在各負荷間的作用肌向心EMGrms並無顯著差異存在。在神經肌肉的活化效果上，LCMJ與LSJ之間的向心EMGrms皆無顯著差異，但因LCMJ向心速度快，其MDF均顯著高於LSJ，且LCMJ離心期的EMGrms隨負荷的增加而顯著增加。可見，負重增強式動作的主要神經力學效應在於增加離心期運動單位的徵召量，並在向心期激發高頻快縮肌運動單位參與收縮。
由本研究結果推論：負荷重量的大小是運動單位徵召量的主要決定因素，而運動單位激發頻率的高低主要取決於動作速度的快慢。因此，訓練過程必須兼顧強化運動單位徵召效果的重量負荷與強化高頻快縮肌運動單位參與收縮的速度負荷，兩者兼顧，以發揮最大的神經力學效應。而若以負重增強式動作來訓練肌力與爆發力，建議以漸增負荷至30%來訓練。
關鍵字：增強式訓練，增強式重量訓練，肌電圖，生物力學，神經力學。

Neuromechanical Analysis of Loaded Plyometric Exercise on Lower Limbs in Elite Female Volleyball Players.
Abstract
Loaded plyometric exercise (LPE) is a type of power training method which combines the advantages of both weight training and plyometric training. The purposes of this study were to investigate the neuromechanical advantages and effects of the loaded counter-movement jump (LCMJ, a typical type of LPE) on lower-limb’s power output, neuromuscular activation, recruitment and firing frequency of motor units (MU) under varied loads.
Twelve elite female volleyball players (age: 19.9±1.1, height: 171.8±6.8 cm, weight: 64.83±6.03 kg), who won the championship of University Volleyball Games in Taiwan in 2004, participated in this experiment. Firstly, maximal isometric force (MIF) of each subject on lower limbs was measured on Kistler’s Quattro Jump force plate, as the setting basis of different load intensity. They perform LCMJ and LSJ (loaded squat jump) on Smith Machine with different load (0%, 10%, 20%, 30%, and 40% of their MIF) randomly. Furthermore, force plate, displacement meter and Biovision’s EMG System were designed to synchronously collect the signals of force, displacement and EMG. Then relevant neuromechanical parameters were read for further analysis with DASYLab and Acqknowledge software. The collection of EMG’s data includes rectus femoris, vastus lateralis, soleus, gastrocnemius lateral head, hamstrings, and tibialis anterior. The standardizing root mean square of EMG (EMGrms) was aimed to assess the amount of MU recruited, and survey the recruit frequency and type of MU by median frequency (MDF). Statistical method adopted Two-way ANOVA to test the differences between different loads and motions on neuromechanical parameters.
The result of this study shows: Loaded plyometric exercise has biomechanical advantage on power output. LCMJ is superior to LSJ evidently, and the advantage increases with increasing load. But in the advantage of neural innervations factor, it is affected by both load and movement speed, along with existent individual differences, which leads to the EMGrms of LCMJ showing no significant difference among different loads during concentric contraction. On the effects of neuromuscular activation, LCMJ and LSJ have not shown obvious difference on EMGrms during concentric phase, but LCMJ is higher significantly than LSJ on MDF due to the faster concentric velocity, and EMGrms of LCMJ increases with increasing load during eccentric phase. It is obvious, the main neuromechanical effect of the loaded plyometric exercise lies in increasing the recruitment of motor units during eccentric contraction, and activating the high-frequency fast-twitch muscles of motor units to participated in concentric contraction.
In conclusion, weight load is the main decisive factor of MU recruited, and the firing frequency of MU depends on speed load mainly. Therefore, in order to inspire the best neuromechanical effects, strength training must give consideration to both the weight load that strengthens MU recruited and the speed load that intensifies higher MU firing frequency, and 30% of their MIF progressively was suggested when performs LPE.
Keyword: plyometric training; plyometric weight training; electromyography; biomechanics; neuromechanics.

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