Bernstein Center Freiburg, University of Freiburg, Freiburg im Breisgau, Germany.
Faculty of Biology, University of Freiburg, Freiburg im Breisgau, Germany.
Sci Rep. 2024 Sep 4;14(1):20634. doi: 10.1038/s41598-024-69353-z.
The redundancy present within the musculoskeletal system may offer a non-invasive source of signals for movement augmentation, where the set of muscle activations that do not produce force/torque (muscle-to-force null-space) could be controlled simultaneously to the natural limbs. Here, we investigated the viability of extracting movement augmentation control signals from the muscles of the wrist complex. Our study assessed (i) if controlled variation of the muscle activation patterns in the wrist joint's null-space is possible; and (ii) whether force and null-space cursor targets could be reached concurrently. During the null-space target reaching condition, participants used muscle-to-force null-space muscle activation to move their cursor towards a displayed target while minimising the exerted force as visualised through the cursor's size. Initial targets were positioned to require natural co-contraction in the null-space and if participants showed a consistent ability to reach for their current target, they would rotate 5 incrementally to generate muscle activation patterns further away from their natural co-contraction. In contrast, during the concurrent target reaching condition participants were required to match a target position and size, where their cursor position was instead controlled by their exerted flexion-extension and radial-ulnar deviation, while its size was changed by their natural co-contraction magnitude. The results collected from 10 participants suggest that while there was variation in each participant's co-contraction behaviour, most did not possess the ability to control this variation for muscle-to-force null-space virtual reaching. In contrast, participants did show a direction and target size dependent ability to vary isometric force and co-contraction activity concurrently. Our results indicate the limitations of using the muscle-to-force null-space activity of joints with a low level of redundancy as a possible command signal for movement augmentation.
骨骼肌肉系统中的冗余可能为运动增强提供一种非侵入性的信号源，其中不会产生力/扭矩的肌肉激活集（肌肉-力零空间）可以与自然肢体同时控制。在这里，我们研究了从腕复合体肌肉中提取运动增强控制信号的可行性。我们的研究评估了：(i) 腕关节零空间中肌肉激活模式的受控变化是否可行；以及 (ii) 是否可以同时达到力和零空间光标目标。在零空间目标到达条件下，参与者使用腕关节零空间中的肌肉-力零空间肌肉激活来移动光标以接近显示的目标，同时通过光标大小最小化施加的力。初始目标的位置需要在零空间中进行自然协同收缩，如果参与者表现出持续达到当前目标的能力，他们将以 5 的增量旋转，以生成远离其自然协同收缩的肌肉激活模式。相比之下，在同时达到目标的条件下，参与者需要匹配目标位置和大小，其中他们的光标位置由他们施加的屈伸和桡尺偏来控制，而其大小则由他们的自然协同收缩幅度改变。从 10 名参与者收集的结果表明，虽然每个参与者的协同收缩行为都存在差异，但大多数参与者都不具备控制肌肉-力零空间虚拟到达的这种变化的能力。相比之下，参与者确实表现出了一种依赖于方向和目标大小的能力，可以同时改变等长力和协同收缩活动。我们的结果表明，在低冗余关节中使用肌肉-力零空间活动作为运动增强的可能命令信号存在局限性。
