Chair of Human Movement Science, Department of Sport and Health Sciences, Technical University of Munich, Munich, Germany.
Department of Neurology, Cantonal Hospital of St. Gallen, St. Gallen, Switzerland.
J Neurophysiol. 2021 May 1;125(5):1663-1680. doi: 10.1152/jn.00499.2020. Epub 2021 Mar 10.
Successful object manipulation requires anticipatory high-level control of finger positions and forces to prevent object slip and tilt. Unlike young adults, who efficiently scale grip forces (GFs) according to surface conditions, old adults were reported to exert excessive grip forces. In this study, we theoretically show how grip force economy depends on the modulation of the centers of pressure on opposing grip surfaces (ΔCoP) according to object properties. In a grasp-to-lift study with young and elderly participants, we investigated how the instruction to lift the object with efficient GF influences the anticipation of torques, ΔCoP and GF control during complex variations of mass distributions and surface properties. Provision of the explicit instruction to strive for force efficiency prompted both age groups to optimize their ΔCoP modulation, although to a lesser degree in the elderly, and also led to a refinement of torque anticipation for a right-sided weight distribution in the young, but not the elderly participants. Consequently, marked drops in GF levels resulted. Furthermore, participants enhanced ΔCoP modulation and lowered GF safety ratios in challenging surface conditions. Higher GF in the elderly was due to decreased skin-surface friction but also worse ΔCoP modulation for lateralized mass distributions when trying to be force efficient. In contrast, safety margins were not elevated in the elderly, suggesting preserved GF control. Our findings demonstrate how task goals influence high-level motor control of object manipulation differentially in young and elderly participants and highlight the necessity to control for both instructions and friction when investigating GF control. Previous studies have shown that forces are covaried as a function of centers of pressure (CoPs) to exert adequate torques. Here, we demonstrate that force-efficient object manipulation requires the modulation of CoPs and show that providing the instruction to be force efficient and challenging surface conditions elicits a GF safety ratio reduction as well as an optimization of anticipatory CoP modulation and torques in the young and, to a lesser degree, in the elderly.
成功的物体操控需要对手指位置和力量进行前瞻性的高级控制，以防止物体滑动和倾斜。与能够根据表面条件有效调整握力（GF）的年轻人不同，老年人被报道会施加过度的握力。在这项研究中，我们从理论上展示了握力经济性如何取决于根据物体特性对手掌压力中心（CoP）的调制。在一项涉及年轻人和老年人参与者的抓握提起研究中，我们研究了在质量分布和表面特性的复杂变化下，用有效 GF 提起物体的指令如何影响力矩、CoP 和 GF 控制的预测。提供努力实现力效率的明确指令促使两个年龄组优化其 CoP 调制，尽管老年人的程度较小，并且还导致年轻人对右侧重量分布的力矩预测得到改进，但老年人参与者则不然。因此，GF 水平明显下降。此外，参与者在具有挑战性的表面条件下增强了 CoP 调制并降低了 GF 安全比。老年人的 GF 较高是由于皮肤-表面摩擦力降低，但在试图实现力效率时，侧向质量分布的 CoP 调制也较差。相比之下，老年人的安全裕度并没有提高，这表明 GF 控制得到了保留。我们的研究结果表明，任务目标如何在年轻人和老年人参与者中对物体操控的高级运动控制产生不同的影响，并强调在研究 GF 控制时需要控制指令和摩擦力。以前的研究表明，力是根据 CoP 变化的，以施加足够的力矩。在这里，我们证明了力效率高的物体操控需要 CoP 的调制，并表明提供力效率和具有挑战性的表面条件的指令会导致 GF 安全比降低，以及年轻人的前瞻性 CoP 调制和力矩的优化，在一定程度上，老年人也是如此。
