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Mechanism of Leg Stiffness Adjustment for Children Landing on Surfaces of Different stiffnesses and Influence on Landing Biomechanics
本研究以國小六年級男性學童10名為受試者，平均身高、體重、年齡分別為155.3 ± 8.2公分、48.0 ± 10.5公斤和11.9 ± 0.3歲。實驗使用Redlake高速攝影機(250Hz)、Kistler 9287型測力板(1000Hz)和Biovision肌電系統(1000Hz)同步收集運動學、地面反作用力和肌電訊號等資料，並運用動力學逆過程(Inverse Dynamics)的方法算出下肢各關節的內力、力矩及作功量。之後使用皮爾遜積差相關法來檢驗下肢勁度與下肢各關節勁度間的相關性，以確定影響下肢勁度之機轉；而不同緩衝時間及不同軟硬地墊所測得之運動學、動力學和肌電的資料經過分組及分析處理之後，使用重複量數二因子變異數分析檢定其差異的顯著性(a =.05)，當達到顯著差異時，再使用薛費法加以事後比較。
According to the papers, humans do adjust their leg stiffness to accommodate changes in stride frequency or surface stiffness, while hopping in places or running forward. The purpose of this study was to determine the mechanisms by which humans adjust leg stiffness during drop landing on surfaces of different stiffnesses, and analyzed the kinematic, kinetic and EMG differences. Ten male six-grade children served as the subjects for this study. The mean height, mass and age were 155.3±8.2 cm, 48.0±10.5 kg and 11.9±0.3 years, respectively. Kinematic, kinetic and EMG data were acquired simultaneously by using a Redlake high speed camera (250Hz) and a Kistler (model 9287) force platform (1000Hz), and a Biovision EMG system (1000Hz). The Inverse Dynamics method was used to acquire the horizontal forces, vertical forces in the three lower extremity joints, net muscle joint moments, muscle joint powers and works done on the extensor muscles of the ankle, knee, and hip joints. The mechanism of leg stiffness adjustment for children landing on surfaces of different stiffnesses was checked using Pearson product-moment correlation between leg stiffness and hip , knee and ankle joint stiffnesses. The selected variables were tested by two-way repeated ANOVA (a = .05) and Scheffe method posterior comparisons. The results could be summarized as following: 1. The leg stiffness was affected by landing time or stiffness of landing surface. The shorter in landing time, or the lower in stiffness of landing surface, the higher in leg stiffness. 2. The mechanisms of leg stiffness adjustment for children landing on surfaces of different stiffnesses in this study were hip and knee joint stiffnesses. 3. There were significant decreases in first peak vertical reaction force, second peak vertical reaction force, the peak vertical force in the three lower extremity joints and the peak moment of knee joint as the landing time increases. Also, there were significant decreases in first peak vertical reaction force, second peak vertical reaction force, the peak horizontal force in the three lower extremity joints, and the time between the moment of landing and first peak vertical reaction force was significant increases as the stiffness of landing surface decreases. So longer landing time or usage of softer mat was suggested when teaching children landing, in order to prevent the possibility of injury.
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