緒論：對於可預期或不可預期的外在環境條件，人體都會存在一種前饋機制來應變劇烈的負荷作用，而著地反彈跳動作的著地前肌肉活化就是重要的反應特徵，然而著地時的可能負荷與接續性的動作則影響了因應肌肉內的協調作用，由於主要的工作肌肉會因應動作的各階段需求進行調整，所以，本研究的主要目的在比較人體不同高度著地反彈跳動作的下肢肌肉活化差異，並探討著地動作的肌肉預收縮現象與自我保護機制特徵。方法：研究以 10名男性大專體育系學生 (身高 167.3 ± 5.4公分、體重 65.1 ± 5.5公斤、年齡 21.7 ± 1.9歲) 為實驗參與者，通過 Biopac MP 150多通道生物訊號擷取系統(2000 Hz) 記錄與分析實驗參與者執行連續直膝跳與 15cm、50cm、100cm著地反彈跳動作的下肢肌肉工作情形，肌肉電訊號均方根振幅經重複量數單因子變異數分析與 HSD事後比較分析。結果：發現隨著高度的增加而增加了肌肉被牽張的負荷，但是也引發了著地前的肌肉預收縮現象與腓腸肌自我保護機制 (p < .05, η2 = .28, power = .72)；著地前與著地瞬間階段，股內側肌在直膝跳、 15cm、50cm與 100cm的比較未達顯著差異；著地後則以股內側肌為主要活化肌群 (p < .05, η2 = .38, power = .90)；著地後的下蹲階段，腓腸肌與比目魚肌在四種高度的比較未達顯著差異。結論：當著地反彈跳的下落高度越高，下肢肌肉會隨著負荷的牽拉而活化程度越高，但是，卻也會由於自我保護機制的功能引發，在更高負荷的神經肌肉工作時，發生肌肉內協調的抑制現象。

INTRODUCTION: The human being exists a feedforward mechanism to response the load extremely under the external condition of anticipation or unanticipation. The muscle pre-activation of bounce drop jump is one kind of the important characteristics. However, the intramuscular coordination of reaction muscle is affected by the magnitude of impact force and the sequence of movement. The purpose of this study was to compare the differences for lower extremity muscle under the manipulations of height of drop jump, and to investigate the muscle activation characteristics of the mechanism of pre-stretch and self-defense during landing. METHODS: The participants (body height: 167.3 ± 5.4 cm, weight: 65.1 ± 5.5kg, age: 21.7 ± 1.9 years old) were ten physical education students. They were asked to perform hop and drop jump (15 cm, 50 cm, and 100 cm). The Biopac MP 150 system (2000 Hz) was used to record and to analysis the muscle activation patterns of lower extremity. The electromyography signals after root mean square processing were compared the statistical difference in repeated measure one way ANOVA and HSD post hoc test. RESULTS: The results showed the phenomena of pre-stretch and the gastrocnemius mechanism of self-defense in the activation patterns were observed clearly with the increasing stretching loads (p < .05, η2 = .28, power = .72). During pre-landing and initial contact phase, the vastus medialis demonstrated no significant difference among hop, 15 cm, 50 cm, and 100 cm. The vastus medialis showed mainly activation muscle during descending phase (p < .05, η2 = .38, power = .90). The gastrocnemius and soleus muscles demonstrated no significant difference during descending phase. CONCLUSION: It indicated that the muscle activation patterns of leg extensors were enhanced following the load increasing of stretch, but the intramuscular coordination mechanism that the activation of neuromuscular was inhibitory appeared to serve as the function of self-defense mechanism.