Relationship between motor unit activity and muscle unit length dining voluntary contractions

为了阐明力量发展与运动单位激活模式之间的关系，本实验采用表面电极法同时观察了人股内侧肌在随意收缩过程中运动单位放电间期和肌单位长度的变化。肌纤维远端的终板有助于准确估计股内侧肌的肌单位长度; 2）肌单位长度缩短>5%~ 15%最大自主收缩率（%MVC）在5%MVC以下持续收缩3 min时，无论峰电位间隔是否延长，肌单位长度均逐渐缩短5%; 4）强直性振动诱发收缩时，肌单位长度逐渐缩短，但缩短量小于随意收缩。这些结果表明，在低-水平可能由运动单位活动和其他相邻运动单位的活动引起。

To elucidate the relationship between force development and activation pattern in motor units, I simultaneously observed the motor unit spike interval and muscle unit length during human voluntary contraction in vastus medialis muscle using surface electrode methods.1)The motor unit action potentials recorded >2 cm from the motor-end plate at the distal end of muscle fibers facilitated accurate estimation of muscle unit length in the vastus medialis muscle.2)The muscle unit length shortened >5% to 15% of maximal voluntary contraction (%MVC). The relationship between spike interval and muscle unit length was not linear.3)Regardless of spike interval elongation, the muscle unit length gradually shortened 5% during the sustained contraction below 5%MVC for 3min.4)The muscle unit length gradually shortened during the evoked contraction from tonic vibration, but the amount of shortening was smaller than that of voluntary contraction.These findings suggested a shortening of muscle unit length during voluntary contraction at a low-level might be caused by both motor unit activity and the activities of other adjacent motor units.