Department of Life Science, The University of Tokyo, Meguro, Tokyo, Japan.
Physiol Rep. 2023 Jun;11(11):e15678. doi: 10.14814/phy2.15678.
The present study aimed to examine the effects of muscle-tendon mechanical properties and electromyographic activity on joint stiffness and jumping height and to explore the determinants of joint stiffness and jumping height. Twenty-nine males performed unilateral drop jumps at three drop heights (10, 20, and 30 cm) using only the ankle joint on the sledge apparatus. Ankle joint stiffness, jumping height, and electromyographic activity of the plantar flexor muscles were measured during drop jumps. Active muscle stiffness of the medial gastrocnemius muscle was calculated according to changes in the estimated muscle force and fascicle length during fast stretching at five different angular velocities (100, 200, 300, 500, and 600 deg s ) after submaximal isometric contractions. Tendon stiffness and elastic energy were measured during ramp and ballistic contractions. Active muscle stiffness was significantly correlated with joint stiffness, except for a few conditions. Tendon stiffness measured during ramp and ballistic contractions was not significantly correlated with joint stiffness. The ratios of electromyographic activity before landing and during the eccentric phase to that during the concentric phase were significantly correlated with joint stiffness. In addition, jumping heights at 10 and 20 cm (except for 30 cm) drop heights were strongly associated with the tendon elastic energy, whereas no other measured variables showed significant correlations with jumping heights. These results suggested that (1) joint stiffness is determined by active muscle stiffness and electromyographic activity patterns during jumping, and (2) jumping height is determined by tendon elastic energy.
本研究旨在探讨肌肉-肌腱力学特性和肌电图活动对关节刚度和跳跃高度的影响，并探讨关节刚度和跳跃高度的决定因素。29 名男性在雪橇装置上仅使用踝关节进行了三次不同下落高度（10、20 和 30cm）的单侧跳下跳。在跳下跳过程中测量了踝关节刚度、跳跃高度和跖屈肌的肌电图活动。根据在亚最大等长收缩后以五个不同角速度（100、200、300、500 和 600°/s）进行快速拉伸过程中估算的肌肉力和肌束长度的变化，计算了内侧腓肠肌的主动肌肉刚度。在斜坡和弹道收缩过程中测量了肌腱刚度和弹性能。主动肌肉刚度与关节刚度显著相关，但有几个条件除外。在斜坡和弹道收缩过程中测量的肌腱刚度与关节刚度没有显著相关性。在着陆前和离心阶段的肌电图活动与向心阶段的肌电图活动的比值与关节刚度显著相关。此外，在 10cm 和 20cm（除 30cm 外）下落高度的跳跃高度与肌腱弹性能量密切相关，而其他测量变量与跳跃高度没有显著相关性。这些结果表明：（1）关节刚度由跳跃过程中的主动肌肉刚度和肌电图活动模式决定；（2）跳跃高度由肌腱弹性能量决定。
