本研究探討肌肉牽張縮短循環（stretch-shortening-cycle, SSC）中20、40和60公分不同高度深跳練習（drop jump, DJ）的地面垂直反作用力曲線的發展，以了解不同牽張速度下SSC練習的力量發展。受試者11名，平均年齡為23.18±2.64歲，身高為173.0±4.03公分，體重為64.31±5.97公斤。本次實驗以AMTI測力板和Penny電子關節角度計測量受試者地面垂直反作用力和膝關節角位移的變化。統計方法採用SPSS統計軟體，以重覆量數單因子變異數分析（α=.05）檢驗這些變數之差異，達顯著差異後再用薛費氏法進行事後比較。 三種不同下跳高度DJ的地面垂直反作用力，離心階段初期，DJ動作產生的被動力量隨著DJ下跳高度的增加而增加，但離心後半階段的主動力量發展卻隨著DJ下跳高度的增加而減少，最後使得三種不同高度DJ所產生的離心末期力量趨於一致。面對SSC高強度動作時，除了可以產生較大的被動力量，必須具備足夠的肌力，才能克服牽張初期負荷並且快速的重新結合橫橋，如同低負荷DJ一樣的發展主動力量，則可以獲得最大離心末期的力量。 由於三種不同高度DJ所產生的離心末期力量差異不大，向心平均力量和騰空高度等運動表現，雖然皆為DJ40>DJ60>DJ20，但差異很小。

This experiment used methods of sport biomechanics to investigate the vertical ground reaction force of drop jumps in order to understand the differences on force development and exercise performance under three different heights of drop jumps. DJ20, DJ40 and dj60 were performed by 11 subjects of jumpers and sprinters with average age 23.18±2.64 years, heights 173.0±4.03cm and weights 64.31±5.97kg. AMIT force-platform and Penny electrical goniometer were used to record ground reaction forces and knee joint angular displacements. The selected variables were tested by one-way repeated ANOVA (α=.05) and scheffe method posterior comparisons. The higher DJ height the larger passive force developed during the beginning of eccentric phase, but the higher DJ height the less active rate of force development during the period of PK2 to the end of pre-stretch. As a result, the force developed at the end of pre-stretch are not different among the three heights of drop jump. As we face the high intensity of SSC movement, the strong strength was required to overcome the high exercise intensity and to reattach the cross bridge as soon as possible which maintain the active rate of force development, and finally increase the force developed at the end of pre-stretch. Because the force of eccentric and are not different among the three heights of drop jumps, the concentric average force and flight heights are also not different among the three heights of drop jumps.