Søgaard K, Christensen H, Jensen B R, Finsen L, Sjøgaard G
National Institute of Occupational Health, Department of Physiology, Copenhagen O, Denmark.
Electroencephalogr Clin Neurophysiol. 1996 Oct;101(5):453-60.
Motor unit (MU) recruitment patterns were studied in 6 female subjects during dynamic contractions at relative workloads corresponding to 10% maximum voluntary contraction. The contractions consisted of a 20 degree elbow flexion (concentric contraction) and extension (eccentric contraction) and MU action potential trains were recorded from the brachial biceps muscle. The mean angular velocity of the dynamic contractions was 10 degrees/s, during which a total of 119 MUs were identified. Additionally, a few contractions were studied at 20 degrees/s during which 30 MUs were identified, and 9 MUs during the 40 degrees/s contraction. About 60% of the identified MUs were active during the concentric as well as the eccentric phase for each of the velocities. Mean firing rate decreased significantly when the contraction changed from concentric to eccentric, whereas the number and properties of identified active MUs were similar. This emphasizes firing rate modulation as important during low level dynamic contractions rather than selective recruitment of different types of MUs in the concentric versus the eccentric phase. Similar kinetic demands occur frequently in occupational tasks, especially during monotonous work. The present data indicate that only a limited pool of MUs are being recruited during such tasks. Extensive recruitment of these MUs may cause fatigue and start a potentially vicious circle leading to work-related muscle disorders.
在6名女性受试者进行动态收缩时，研究了运动单位（MU）的募集模式，收缩强度对应于最大自主收缩的10%。收缩动作包括20度的肘部屈曲（向心收缩）和伸展（离心收缩），并从肱二头肌记录MU动作电位序列。动态收缩的平均角速度为10度/秒，在此期间共识别出119个运动单位。此外，还研究了一些在20度/秒时的收缩，期间识别出30个运动单位，以及在40度/秒收缩时的9个运动单位。在每个速度下，约60%的已识别运动单位在向心和离心阶段均处于活跃状态。当收缩从向心变为离心时，平均放电频率显著降低，而已识别的活跃运动单位的数量和特性相似。这强调了在低强度动态收缩过程中，放电频率调制比在向心与离心阶段选择性募集不同类型的运动单位更为重要。类似的动力学需求在职业任务中经常出现，尤其是在单调工作期间。目前的数据表明，在这类任务中仅募集了有限数量的运动单位。这些运动单位的广泛募集可能会导致疲劳，并引发潜在的恶性循环，进而导致与工作相关的肌肉疾病。
