Axelson H W, Hagbarth K-E
Clinical Neurophysiology, Department of Neuroscience, Uppsala University Hospital, Uppsala, Sweden.
Acta Physiol Scand. 2003 Dec;179(4):389-98. doi: 10.1046/j.0001-6772.2003.01217.x.
Resting tension of relaxed skeletal muscle fibres held at a given length varies with the immediate previous history of length changes and contractions. The primary aim of this study was to explore the motor control consequences of this history-dependency in healthy subjects.
Angular position and passive torque were recorded from the intact wrist joint. Integrated surface electromyography (IEMG) was recorded from wrist extensor and flexor muscles.
In relaxed subjects, wrist joint position was displaced towards dorsiflexion after a single high-amplitude dorsiflexion movement combined with a strong flexor/extensor co-contraction (dorsiflexion conditioning), whereas after volarflexion conditioning there was a shift towards volarflexion. These after-effects could be abruptly cancelled by short periods ( approximately 5 s) of rapid flapping hand movements or forceful isometric co-contractions, findings indicative of muscle thixotropy. The IEMG-evaluated motor after-effects were as follows. A slowly subsiding wrist flexor contraction was needed to restore and maintain the original resting wrist position after dorsiflexion conditioning whereas a slowly subsiding extensor contraction was needed for the same goal after volarflexion conditioning. Furthermore, ongoing wrist extensor IEMG activity required to actively hold the wrist in a moderate dorsiflexed position or to resist a constant volar torque at resting position was temporarily reduced after dorsiflexion conditioning and enhanced (not significantly) after volarflexion conditioning.
The results provide evidence that during voluntary maintenance of a desired wrist joint position the motor commands to the position-holding muscles are unconsciously adjusted to compensate for thixotropy-dependent variations in the resting tension of the muscles.
保持在给定长度的放松骨骼肌纤维的静息张力会随之前长度变化和收缩的历史情况而改变。本研究的主要目的是探究健康受试者中这种历史依赖性对运动控制的影响。
记录完整腕关节的角位置和被动扭矩。记录腕伸肌和屈肌的表面肌电图积分（IEMG）。
在放松的受试者中，单次高幅度背屈运动结合强烈的屈肌/伸肌共同收缩（背屈预处理）后，腕关节位置向背屈方向偏移，而掌屈预处理后则向掌屈方向偏移。这些后效应可通过短时间（约5秒）的快速甩手运动或强力等长共同收缩突然消除，这些发现表明肌肉具有触变性。IEMG评估的运动后效应如下。背屈预处理后，需要缓慢消退的腕屈肌收缩来恢复并维持原始的静息腕关节位置，而掌屈预处理后，为达到相同目的则需要缓慢消退的伸肌收缩。此外，在背屈预处理后，主动将腕关节保持在中度背屈位置或在静息位置抵抗恒定掌侧扭矩所需的持续腕伸肌IEMG活动会暂时降低，而在掌屈预处理后则会增强（不显著）。
结果表明，在自愿维持所需腕关节位置期间，对负责保持位置的肌肉的运动指令会在无意识中进行调整，以补偿肌肉静息张力中依赖触变性的变化。
