Arampatzis A, Brüggemann G P, Klapsing G M
German Sport University of Cologne, Institut for Biomechanics, Carl-Diem-Weg 6, 50933 Cologne, Germany.
Med Sci Sports Exerc. 2001 Jun;33(6):923-31. doi: 10.1097/00005768-200106000-00011.
The purposes of this study were: a) to examine the effect of verbal instructions given to the subjects on the control of lower extremity stiffness and b) to determine the effect of leg stiffness on mechanical energetic processes during drop jumps on a sprung surface.
A total of 10 female athletes performed a series of drop jumps on a sprung surface from heights of 20 and 40 cm. The instructions given to the subjects were a) "jump as high as you can" and b) "jump high a little faster than at your previous jump." The jumps were performed at each height until the athlete could not achieve a shorter ground contact time. Four jumps per subject per height were analyzed. The ground reaction forces were measured using a "Kistler" force plate (1000 Hz). The athletes' body positions were recorded using a high-speed (250 Hz) video camera. The deformation of the sprung surface was determined by another high-speed camera operating at 500 Hz. Surface EMG was used to measure muscle activity in five leg muscles.
The contact time showed high correlation with leg stiffness as well as with ankle and knee stiffness. The change in leg stiffness was not due to the duration of the preactivation but rather to the level of activation during this phase. An increase in leg stiffness caused an increase in the energy stored and recovered in and by the sprung surface and a decrease of the energy produced by the subjects.
By influencing contact time through verbal instructions, it is possible to control leg stiffness. Maximal vertical take-off velocity of the center of mass and maximal take-off body energy can be achieved having different levels of leg stiffness. The maximization of mechanical power is achieved by optimal leg stiffness values and leg muscle preactivation levels.
本研究的目的是：a）检查给予受试者的口头指令对下肢刚度控制的影响；b）确定在弹性表面上进行纵跳时腿部刚度对机械能过程的影响。
共有10名女性运动员在弹性表面上从20厘米和40厘米的高度进行了一系列纵跳。给予受试者的指令是：a）“尽可能跳得高”；b）“比前一次跳跃稍快一点跳得高”。在每个高度进行跳跃，直到运动员无法实现更短的地面接触时间。分析每个受试者每个高度的4次跳跃。使用“奇石乐”测力板（1000赫兹）测量地面反作用力。使用高速（250赫兹）摄像机记录运动员的身体姿势。弹性表面的变形由另一台以500赫兹运行的高速摄像机确定。表面肌电图用于测量五条腿部肌肉的肌肉活动。
接触时间与腿部刚度以及踝关节和膝关节刚度高度相关。腿部刚度的变化不是由于预激活的持续时间，而是由于该阶段的激活水平。腿部刚度的增加导致弹性表面储存和恢复的能量增加，以及受试者产生的能量减少。
通过口头指令影响接触时间，可以控制腿部刚度。在不同的腿部刚度水平下，可以实现质心的最大垂直起跳速度和最大起跳身体能量。通过最佳的腿部刚度值和腿部肌肉预激活水平可以实现机械功率的最大化。
