de Freitas Paulo B, Jaric Slobodan
Human Performance Lab, Department of Health, Nutrition, and Exercise Sciences, University of Delaware, 547 South College Avenue, Newark, DE 19716, USA.
Exp Brain Res. 2009 Apr;194(4):605-18. doi: 10.1007/s00221-009-1738-0. Epub 2009 Feb 27.
We evaluated coordination of the hand grip force (GF; normal component of the force acting at the hand-object contact area) and load force (LF; the tangential component) in a variety of grasping techniques and two LF directions. Thirteen participants exerted a continuous sinusoidal LF pattern against externally fixed handles applying both standard (i.e., using either the tips of the digits or the palms; the precision and palm grasps, respectively) and non-standard grasping techniques (using wrists and the dorsal finger areas; the wrist and fist grasp). We hypothesized (1) that the non-standard grasping techniques would provide deteriorated indices of force coordination when compared with the standard ones, and (2) that the nervous system would be able to adjust GF to the differences in friction coefficients of various skin areas used for grasping. However, most of the indices of force coordination remained similar across the tested grasping techniques, while the GF adjustments for the differences in friction coefficients (highest in the palm and the lowest in the fist and wrist grasp) provided inconclusive results. As hypothesized, GF relative to the skin friction was lowest in the precision grasp, but highest in the palm grasp. Therefore, we conclude that (1) the elaborate coordination of GF and LF consistently seen across the standard grasping techniques could be generalized to the non-standard ones, while (2) the ability to adjust GF using the same grasping technique to the differences in friction of various objects cannot be fully generalized to the GF adjustment when different grasps (i.e., hand segments) are used to manipulate the same object. Due to the importance of the studied phenomena for understanding both the functional and neural control aspects of manipulation, future studies should extend the current research to the transient and dynamic tasks, as well as to the general role of friction in our mechanical interactions with the environment.
我们评估了在各种抓握技术以及两个负载力（LF）方向下，握力（GF；作用于手与物体接触区域的力的法向分量）与负载力（LF；切向分量）的协调性。13名参与者针对外部固定手柄施加连续的正弦LF模式，采用标准抓握技术（即分别使用指尖或手掌；精确抓握和手掌抓握）和非标准抓握技术（使用手腕和手指背侧区域；手腕抓握和握拳抓握）。我们假设：（1）与标准抓握技术相比，非标准抓握技术会使力协调性指标变差；（2）神经系统能够根据用于抓握的不同皮肤区域的摩擦系数差异来调整GF。然而，在测试的抓握技术中，大多数力协调性指标保持相似，而针对摩擦系数差异的GF调整（手掌最高，握拳抓握和手腕抓握最低）结果不明确。如假设的那样，相对于皮肤摩擦力的GF在精确抓握中最低，但在手掌抓握中最高。因此，我们得出结论：（1）在标准抓握技术中始终可见的GF和LF的精细协调性可以推广到非标准抓握技术；（2）使用相同抓握技术针对不同物体的摩擦差异调整GF的能力，不能完全推广到使用不同抓握方式（即手部节段）操纵同一物体时的GF调整。由于所研究现象对于理解操纵的功能和神经控制方面都很重要，未来的研究应将当前研究扩展到瞬态和动态任务，以及摩擦在我们与环境的机械相互作用中的一般作用。
