In response to sudden perturbations of stance stability, muscles of both legs are activated for balance recovery. In conditions that one of the legs has a reduced capacity to respond, the opposite leg is predicted to compensate by responding more powerfully to restore stable upright stance. In this investigation, we aimed to evaluate between-leg compensatory control in automatic postural responses to sudden perturbations in a situation in which plantar flexor muscles of a single leg were fatigued. Young participants were evaluated in response to a series of perturbations inducing forward body sway, with a focus on activation of plantar flexor muscles: lateral and medial gastrocnemii and soleus. Muscular responses were analyzed through activation magnitude and latency of muscular activation onset. For evaluation of balance and postural stability, we also analyzed the center of pressure and upper trunk displacement and weight-bearing asymmetry between the legs. Responses were assessed in three conditions: pre-fatigue, under single-leg fatigue, and following the recovery of muscular function. Results showed (a) compensation of the non-fatigued leg through the increased magnitude of muscular activation in the first perturbation under fatigue; (b) adaptation in the non-fatigued leg over repetitive perturbations, with a progressive decrement of muscular activation over trials; and (c) maintenance of increased muscular activation of the non-fatigued leg following fatigue dissipation. These findings suggest that the central nervous system is able to modulate the descending motor drive individually for each leg’s muscles apparently based on their potential contribution for the achievement of the behavioral aim of recovering stable body balance following stance perturbations.

响应于姿态稳定性的突然扰动，双腿的肌肉被激活以恢复平衡。在其中一条腿的响应能力降低的情况下，预计另一条腿会通过更强大的响应来补偿，以恢复稳定的直立姿势。在这项研究中，我们旨在评估单腿足屈肌疲劳时对突然扰动的自动姿势响应中的腿间补偿控制。对年轻参与者进行了评估，以应对一系列诱发身体向前摇摆的扰动，重点是激活flex屈肌：外侧腓肠肌和比目鱼肌。通过活化程度和肌肉活化发作的潜伏期来分析肌肉反应。为了评估平衡和姿势稳定性，我们还分析了双腿之间的压力中心，上躯干位移和承重不对称性。在三种情况下评估反应：疲劳前，单腿疲劳下以及肌肉功能恢复后。结果显示：（a）在疲劳下的第一次扰动中，通过增加肌肉激活程度来补偿无疲劳腿。（b）在无疲劳的腿部适应反复的扰动，并在试验中逐渐减少肌肉的活动；（c）在疲劳消散后，保持无疲劳腿的肌肉活化作用增强。