Movement Neuroscience Laboratory, Department of Physical Therapy, Movement, and Rehabilitation Sciences, Northeastern University, Boston, MA, 02115, USA.
Faculty of Sport Sciences, Sivas Cumhuriyet University, Sivas, Turkey.
Exp Brain Res. 2024 Mar;242(3):675-683. doi: 10.1007/s00221-023-06774-8. Epub 2024 Jan 23.
The purpose of the study was to investigate the influence of contraction history on force steadiness and the associated EMG activity during submaximal isometric contractions performed with the dorsiflexor muscles. The key feature of the protocol was a triangular ramp contraction performed in the middle of a steady contraction at a lower target force. The target force during the ramp contraction was 20% MVC greater than that during the steady contraction. Thirty-seven healthy individuals (21 men and 16 women) performed the submaximal tasks with the ankle dorsiflexors. Electromyography (EMG) signals were recorded from tibialis anterior with a pair of surface electrodes. The coefficient of variation for force was significantly greater during the second steady contraction compared with the first one at each of the seven target forces (p < 0.015; d = 0.38-0.92). Although the average applied force during the steady contractions before and after the triangular contraction was the same (p = 0.563), the mean EMG amplitude for the steady contractions performed after the triangular contraction was significantly greater at each of the seven target forces (p < 0.0001; d = 0.44-0.68). Also, there were significant differences in mean EMG frequency between the steady contractions performed before and after the triangular contraction (p < 0.01; d = 0.13-0.82), except at 10 and 20% MVC force. The greater force fluctuations during a steady submaximal contraction after an intervening triangular contraction indicate a change in the discharge characteristics of the involved motor units.
本研究旨在探讨收缩历史对腓肠肌进行亚最大等长收缩时力稳定性的影响以及相关的肌电图（EMG）活动。该方案的一个关键特征是在较低目标力的稳定收缩期间进行三角形斜坡收缩。斜坡收缩期间的目标力比稳定收缩期间的目标力高 20%最大收缩力（MVC）。37 名健康个体（21 名男性和 16 名女性）进行了踝关节背屈肌的亚最大任务。用一对表面电极从胫骨前肌记录肌电图（EMG）信号。在七个目标力中的每一个上，第二次稳定收缩期间的力变异系数与第一次相比显著更大（p<0.015；d=0.38-0.92）。尽管在三角收缩前后的稳定收缩期间平均施加的力相同（p=0.563），但在三角收缩后的稳定收缩期间的平均 EMG 幅度在七个目标力中的每一个上都显著更大（p<0.0001；d=0.44-0.68）。此外，在三角收缩前后的稳定收缩期间，平均 EMG 频率也存在显著差异（p<0.01；d=0.13-0.82），除了在 10%和 20%MVC 力下。在三角收缩后的稳定亚最大收缩期间，力波动较大表明参与的运动单位的放电特征发生了变化。
