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

为了阐明运动单元的力量发展与激活模式之间的关系，我使用表面电极方法同时观察了人股内侧肌随意收缩时的运动单元尖峰间隔和肌肉单元长度。1)在肌纤维远端运动端板处记录的运动单位动作电位，有助于准确估计股内侧肌的肌肉单位长度。2)肌肉单位长度缩短>最大自主收缩（%MVC）的5% ~ 15%。刺突间隔与肌单位长度之间不是线性关系。3)不考虑峰间伸长，在低于5% mvc持续收缩3min时，肌单位长度逐渐缩短5%。4)强直振动诱发收缩时，肌单位长度逐渐缩短，但缩短量小于自主收缩。这些发现表明，在低水平的自主收缩过程中，肌肉单位长度的缩短可能是由运动单位活动和其他邻近运动单位的活动引起的。

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.