Mancebo Felipe D, Cabral Hélio V, de Souza Leonardo M L, de Oliveira Liliam F, Vieira Taian M
Laboratório de Biomecânica, Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
Laboratório de Biomecânica, Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
J Electromyogr Kinesiol. 2019 Jun;46:8-13. doi: 10.1016/j.jelekin.2019.03.002. Epub 2019 Mar 7.
Changes in innervation zone (IZ) position may affect the amplitude of surface electromyograms (EMGs). If not accounted for, these changes may lead to equivocal interpretation on the degree of muscle activity from EMG amplitude. In this study we ask how much the IZ position changes within different regions of the pectoralis major (PM) during the bench press exercise. If expressive, changes in IZ position may explain the conflictual results reported on PM activation during bench press. Single-differential surface EMGs were collected from 15 regions along the PM cranial, centro-cranial, centro-caudal and caudal fibres, while 11 healthy participants gently, isometrically contracted their muscle. IZs were identified visually, from EMGs collected with the glenohumeral joint at extreme bench press positions; 20° and 110° of abduction in the horizontal plane. Except for 3 out of 88 acquisitions (4 detection sites × 2 glenohumeral angles × 11 participants), for which no phase opposition and action potential propagation were observed, IZs could be well identified. Group results revealed the IZ moved medially from 110° to 20° of glenohumeral joint abduction in the horizontal plane, regardless of the PM region from where EMGs were detected (P < 0.01). IZs were confined medially within PM, from ∼20% to ∼40% of the muscle-tendon unit length, and their position changed up to 13.3%. These results suggest that changes in the amplitude of EMGs detected mainly medially from PM may be not associated with changes in the degree of PM activity during bench press.
神经支配区（IZ）位置的变化可能会影响表面肌电图（EMG）的幅度。如果不加以考虑，这些变化可能会导致对EMG幅度所反映的肌肉活动程度产生模棱两可的解释。在本研究中，我们探究了在卧推运动过程中，胸大肌（PM）不同区域内IZ位置的变化程度。如果变化明显，IZ位置的改变可能解释了关于卧推过程中PM激活的矛盾结果。从沿着PM头侧、头中央、尾中央和尾侧纤维的15个区域采集单差表面肌电图，同时11名健康参与者进行轻度等长肌肉收缩。通过在卧推极端位置（水平面外展20°和110°）采集的EMG，目视识别IZ；除了88次采集（4个检测部位×2个盂肱关节角度×11名参与者）中有3次未观察到相位相反和动作电位传播外，IZ均可被很好地识别。组内结果显示，无论从哪个PM区域检测EMG，在水平面内，IZ在盂肱关节外展从110°到20°的过程中均向内侧移动（P<0.01）。IZ局限于PM内侧，位于肌腱单位长度的约20%至约40%范围内，其位置变化高达13.3%。这些结果表明，主要从PM内侧检测到的EMG幅度变化可能与卧推过程中PM活动程度的变化无关。
