Data from: Precision grip control while walking down a stair step

The aim of this study was to determine whether the internal model regulating grip force (GF)/load force (LF) coordination during a brisk load increase is preserved when the lower extremities produce a perturbation during a single step-down task. We observed the coordination of the vertical ground reaction force (vGRF), GF and LF while holding a handheld object during a single step-down task. The 3 forces (vGRF, GF and LF) decreased during the start of the task. While the subject was descending, LF and GF became dissociated from vGRF and increased in value, probably to anticipate the first foot contact. Coordination of LF and GF was maintained until the maximal vGRF (knee extension). LF peaked in the same time window as vGRF, whereas GF peaked about 70 ms later. This desynchronization, which was previously observed in direct load increase on a handheld object, was interpreted to be a predictive action to ensure the smooth management of the brisk increase in load induced by the lower extremities. Incidentally, in this group, kinematic and dynamic differences were observed between men and women, which may highlight a gender-specific strategy to perform the step-down task. In conclusion, these results suggest that the internal model of precision grip is able to integrate a brisk load change, whatever its origin, and regulate the forces to provide an ideal GF to dampen a brisk load increase and secure the object.

本研究旨在探究快速载荷增加过程中调控握力（grip force, GF）/载荷力（load force, LF）协调的内部模型，在下肢于单腿下台阶任务（single step-down task）中产生扰动时是否仍可保持稳定。我们在受试者完成单腿下台阶任务并手持物体的过程中，观测了垂直地面反作用力（vertical ground reaction force, vGRF）、握力与载荷力的协调变化特征。任务启动初期，上述三种力（vGRF、GF与LF）均出现下降。当受试者向下台阶移动时，载荷力与握力脱离与垂直地面反作用力的关联并出现数值升高，这大概率是为了预判首次足部触地动作。载荷力与握力的协调关系始终维持至垂直地面反作用力达到峰值（膝关节伸展时刻）。载荷力的峰值出现时间与垂直地面反作用力的峰值窗口重合，而握力的峰值则滞后约70毫秒。这种此前在手持物体直接加载实验中观测到的去同步现象，被解读为一种预测性动作，旨在平稳管控由下肢活动引发的快速载荷增量。顺带一提，本研究队列中观察到男性与女性受试者在运动学与动力学特征上存在差异，这或许体现了完成单腿下台阶任务的性别特异性策略。综上，本研究结果表明，精准握力的内部模型能够整合任意来源的快速载荷变化，并通过调控相关力的输出，提供适配的握力以缓冲快速载荷增量、确保手持物体的握持安全。