Arm cycling is a bi-manual motor task used in medical rehabilitation and in sports training. Understanding how muscle coordination changes across different biomechanical constraints in arm cycling is a step towards improved rehabilitation approaches. This exploratory study aims to get new insights on motor control during arm cycling. To achieve our main goal, we used the muscle synergies analysis to test three hypotheses: 1) body position with respect to gravity (sitting and supine) has an effect on muscle synergies; 2) the movement size (crank length) has an effect on the synergistic behavior; 3) the bimanual cranking mode (asynchronous and synchronous) requires different synergistic control. Thirteen able-bodied volunteers performed arm cranking on a custom-made device with unconnected cranks, which allowed testing three different conditions: body position (sitting versus supine), crank length (10cm versus 15cm) and cranking mode (synchronous versus asynchronous). For each of the eight possible combinations, subjects cycled for 30 seconds while electromyography of 8 muscles (4 from each arm) were recorded: biceps brachii, triceps brachii, anterior deltoid and posterior deltoid. Muscle synergies in this 8-dimensional muscle space were extracted by non-negative matrix factorization. Four synergies accounted for over 90% of muscle activation variances in all conditions. Results showed that synergies were affected by body position and cranking mode but practically unaffected by movement size. These results suggest that the central nervous system may employ different motor control strategies in response to external constraints such as cranking mode and body position during arm cycling.

中文翻译：

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重力和运动学约束对手臂自行车肌肉协同作用的影响。

手臂骑行是一种双手动运动任务，用于医疗康复和运动训练。了解手臂骑行中不同生物力学约束下肌肉协调如何变化是朝着改进康复方法迈出的一步。这项探索性研究旨在获得有关手臂骑行期间运动控制的新见解。为了实现我们的主要目标，我们使用肌肉协同分析来检验三个假设：1) 相对于重力的身体姿势（坐姿和仰卧）对肌肉协同作用有影响；2）运动大小（曲柄长度）对协同行为有影响；3）手动盘车模式（异步和同步）需要不同的协同控制。13 名身体健全的志愿者在带有未连接曲柄的定制设备上进行手臂曲柄转动，这允许测试三种不同的条件：身体位置（坐姿与仰卧）、曲柄长度（10 厘米与 15 厘米）和曲柄模式（同步与异步）。对于八种可能的组合中的每一种，受试者循环 30 秒，同时记录 8 块肌肉（每只手臂 4 块）的肌电图：肱二头肌、肱三头肌、前三角肌和后三角肌。通过非负矩阵分解来提取这个 8 维肌肉空间中的肌肉协同作用。在所有条件下，四种协同作用占肌肉激活差异的 90% 以上。结果表明，协同作用受身体位置和曲柄模式的影响，但实际上不受运动大小的影响。这些结果表明，中枢神经系统可能会采用不同的运动控制策略来响应外部约束，例如手臂循环期间的摇动模式和身体位置。