Muscle synergies reflect the presence of a common neural input to multiple muscles. Steering small sets of synergies is commonly believed to simplify the control of complex motor tasks like walking and running. When these locomotor patterns emerge, it is likely that synergies emerge as well. We hence hypothesized that in children learning to run the number of accompanying synergies increases and that some of the synergies’ activities display a temporal shift related to a reduced stance phase as observed in adults. We investigated the development of locomotion in 23 children aged 2-9 years of age and compared them with seven young adults. Muscle activity of 15 bilateral leg, trunk, and arm muscles, ground reaction forces, and kinematics were recorded during comfortable treadmill walking and running, followed by a muscle synergy analysis. We found that toddlers (2-3.5 yrs) and preschoolers (3.5-6.5 yrs) utilize a “walk-run strategy” when learning to run: they managed the fastest speeds on the treadmill by combining double support and flight phases. In particular the activity duration of the medial gastrocnemius muscle was weakly correlated with age. The number of synergies across groups and conditions needed to cover sufficient data variation ranged between four and eight. The number of synergies tended to be smaller in toddlers than it did in preschoolers and school-age children but the adults had the lowest number for both conditions. Against our expectations, the age groups did not differ significantly in the timing or duration of synergies. We believe that the increase in the number of muscle synergies in older children relates to motor learning and exploration. The ability to run with a flight phase is clearly associated with an increase in the number of muscle synergies.

中文翻译：

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在跑步机上行走和奔跑的孩子的肌肉协同作用

肌肉协同作用反映了对多块肌肉存在共同的神经输入。普遍认为，引导少量协同效应可以简化对复杂的运动任务（如步行和跑步）的控制。当这些运动模式出现时，可能也会产生协同作用。因此，我们假设在儿童中学习运行协同作用的数量增加，并且某些协同作用的活动显示出与成人所观察到的姿势阶段减少有关的时间变化。我们调查了23名2至9岁儿童的运动发育情况，并将其与7位年轻成年人进行了比较。在舒适的跑步机上行走和跑步期间，记录了15条双侧腿，躯干和手臂肌肉的肌肉活动，地面反作用力和运动学，然后进行了肌肉协同作用分析。我们发现，幼儿（2-3.5岁）和学龄前儿童（3.5-6.5岁）在学习跑步时会采用“步行跑步策略”：他们通过结合双重支持和飞行阶段来控制跑步机上最快的速度。特别是内侧腓肠肌的活动时间与年龄呈弱相关。涵盖足够的数据变化所需的跨组和条件的协同作用的数量在四个到八个之间。与学龄前儿童和学龄儿童相比，幼儿的协同作用数量趋于减少，但在这两种情况下，成年人的协同作用数量最低。超出我们的预期，不同年龄段的协同作用的时间或持续时间没有显着差异。我们认为，年龄较大的儿童的肌肉协同作用数量的增加与运动学习和探索有关。