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.

该研究的目的是调查背屈肌进行次最大等长收缩时收缩历史对力稳定性和相关肌电图活动的影响。该协议的关键特征是在较低目标力的稳定收缩中间进行三角斜坡收缩。斜坡收缩期间的目标力比稳定收缩期间的目标力大 20% MVC。 37 名健康人（21 名男性和 16 名女性）用踝背屈肌执行了次最大任务。用一对表面电极记录胫骨前肌的肌电图（EMG）信号。与第一次稳定收缩相比，在七个目标力中，第二次稳定收缩期间力的变异系数明显更大（ p < 0.015； d = 0.38–0.92）。尽管三角收缩之前和之后稳定收缩期间的平均施加力相同 ( p = 0.563)，但三角收缩之后执行的稳定收缩的平均 EMG 振幅在七个目标力中的每一个上都显着更大 ( p < 0.0001； d = 0.44–0.68)。此外，除了 10% 和 20% MVC 力外，三角收缩之前和之后进行的稳定收缩之间的平均 EMG 频率存在显着差异（ p < 0.01； d = 0.13–0.82）。在介入的三角收缩之后的稳定次最大收缩期间更大的力波动表明所涉及的运动单元的放电特性的变化。