Ludvig Daniel, Whitmore Mariah W, Perreault Eric J
Department of Biomedical Engineering, Northwestern University, Evanston, IL, United States.
Shirley Ryan AbilityLab, Chicago, IL, United States.
Front Integr Neurosci. 2022 Mar 21;16:802608. doi: 10.3389/fnint.2022.802608. eCollection 2022.
Behaviors we perform each day, such as manipulating an object or walking, require precise control of the interaction forces between our bodies and the environment. These forces are generated by muscle contractions, specified by the nervous system, and by joint mechanics, determined by the intrinsic properties of the musculoskeletal system. Depending on behavioral goals, joint mechanics might simplify or complicate control of movement by the nervous system. Whether humans can exploit joint mechanics to simplify neural control remains unclear. Here we evaluated if leveraging joint mechanics simplifies neural control by comparing performance in three tasks that required subjects to generate specified torques about the ankle during imposed sinusoidal movements; only one task required torques that could be generated by leveraging the intrinsic mechanics of the joint. The complexity of the neural control was assessed by subjects' perceived difficulty and the resultant task performance. We developed a novel approach that used continuous estimates of ankle impedance, a quantitative description of the joint mechanics, and measures of muscle activity to determine the mechanical and neural contributions to the net ankle torque generated in each task. We found that the torque resulting from changes in neural control was reduced when ankle impedance was consistent with the task being performed. Subjects perceived this task to be easier than those that were not consistent with the impedance of the ankle and were able to perform it with the highest level of consistency across repeated trials. These results demonstrate that leveraging the mechanical properties of a joint can simplify task completion and improve performance.
我们每天执行的行为，如操纵物体或行走，都需要精确控制我们身体与环境之间的相互作用力。这些力由肌肉收缩产生，由神经系统指定，并由关节力学决定，而关节力学由肌肉骨骼系统的固有属性决定。根据行为目标，关节力学可能会简化或复杂化神经系统对运动的控制。人类是否能够利用关节力学来简化神经控制仍不清楚。在这里，我们通过比较三项任务的表现来评估利用关节力学是否能简化神经控制，这三项任务要求受试者在施加正弦运动时在踝关节周围产生特定扭矩；只有一项任务需要通过利用关节的固有力学来产生扭矩。神经控制的复杂性通过受试者感知的难度和最终的任务表现来评估。我们开发了一种新颖的方法，该方法使用踝关节阻抗的连续估计值（对关节力学的定量描述）以及肌肉活动的测量值，来确定每项任务中产生的净踝关节扭矩的机械和神经贡献。我们发现，当踝关节阻抗与所执行的任务一致时，神经控制变化所产生的扭矩会降低。受试者认为这项任务比那些与踝关节阻抗不一致的任务更容易，并且能够在重复试验中以最高的一致性完成它。这些结果表明，利用关节的机械特性可以简化任务完成并提高表现。
