Forman Davis A, Baarbé Julianne, Daligadu Julian, Murphy Bernadette, Holmes Michael W R
Faculty of Health Sciences, University of Ontario Institute of Technology, Oshawa, ON, Canada.
Faculty of Health Sciences, University of Ontario Institute of Technology, Oshawa, ON, Canada.
J Electromyogr Kinesiol. 2016 Apr;27:95-101. doi: 10.1016/j.jelekin.2016.02.005. Epub 2016 Feb 23.
Variations in handgrip force influences shoulder muscle activity, and this effect is dependent upon upper limb position. Previous work suggests that neural coupling between proximal and distal muscles with changes in joint position is a possible mechanism but these studies tend to use artificially constrained postures that do not reflect activities of daily living. The purpose of this study was to examine the effects of upper limb posture on corticospinal excitability to the forearm muscles during workplace relevant arm positions. Motor evoked potentials (MEPs) were elicited in four forearm muscles via transcranial magnetic stimulation at six arm positions (45°, 90° and 120° of humeral elevation in both the flexion and abduction planes). MEPs were delivered as stimulus-response curves (SRCs) at rest and at constant intensity during two gripping tasks. Boltzmann plateau levels were smaller for the flexor carpi radialis in flexion at 45° versus 90° (p=0.0008). Extensor carpi radialis had a greater plateau during flexion than abduction (p=0.0042). Corticospinal excitability to the forearm muscles were influenced by upper limb posture during both the resting and gripping conditions. This provides further evidence that upper limb movements are controlled as a whole rather than segmentally and is relevant for workplace design considerations.
握力的变化会影响肩部肌肉活动，且这种影响取决于上肢的位置。先前的研究表明，随着关节位置变化，近端和远端肌肉之间的神经耦合是一种可能的机制，但这些研究往往使用人工限制的姿势，无法反映日常生活活动。本研究的目的是在与工作场所相关的手臂位置期间，检查上肢姿势对前臂肌肉皮质脊髓兴奋性的影响。通过在六个手臂位置（屈曲和外展平面中肱骨抬高45°、90°和120°）进行经颅磁刺激，在四块前臂肌肉中引出运动诱发电位（MEP）。在两项抓握任务中，MEP以刺激-反应曲线（SRC）的形式在静息状态和恒定强度下发放。桡侧腕屈肌在45°屈曲时的玻尔兹曼平台水平比90°屈曲时小（p = 0.0008）。桡侧腕伸肌在屈曲时的平台水平比外展时大（p = 0.0042）。在静息和抓握状态下，上肢姿势均会影响前臂肌肉的皮质脊髓兴奋性。这进一步证明上肢运动是作为一个整体而非分段进行控制的，这对于工作场所设计考虑具有重要意义。
