de Freitas Paulo B, Uygur Mehmet, Jaric Slobodan
Department of Health, Nutrition, and Exercise Sciences, University of Delaware, 547 S. College Avenue, Newark, DE 19716, USA.
Neurosci Lett. 2009 Jun 19;457(1):16-20. doi: 10.1016/j.neulet.2009.03.108. Epub 2009 Apr 7.
The aim of the study was to evaluate grip force (GF; normal component of hand-object interaction) adaptation across different manipulation conditions. We hypothesized (1) that the absolute safety margin (the difference between the exerted GF and the minimum GF that prevents slippage; absolute SM), rather than the relative SM (the same difference relative to the minimum GF required), could be an invariant feature of manipulation, as well as (2) that the SM would be higher in static than in dynamic tasks. Fourteen participants performed the free holding and the static holding tasks that required a same pulling force. Each task was performed using a variety of grasps and two different object coatings that both provided different frictions acting between the hand and the hand-held object. Both tasks revealed an increase in the relative SM associated with an increase in friction, while the absolute SM either remained unchanged (free holding) or suggested a moderate negative relationship (static holding task). Both relative and absolute SM were also higher in the free holding than in the static holding. The later result could be a consequence of the task mechanical conditions (i.e., dynamic vs. static), rather than of the difference in neural control mechanisms (feedback vs. feed-forward, respectively). The obtained findings suggest that the absolute SM (rather than the relative one) should be used in future studies of hand force coordination in healthy and clinical populations, while GF adaptation obtained from static and dynamic manipulation tasks should be separately assessed.
本研究的目的是评估在不同操作条件下握力（GF；手部与物体相互作用的法向分量）的适应性。我们假设：（1）绝对安全裕度（即施加的握力与防止打滑所需的最小握力之间的差值；绝对SM）而非相对安全裕度（相对于所需最小握力的相同差值）可能是操作的一个不变特征；以及（2）在静态任务中安全裕度会高于动态任务。14名参与者进行了需要相同拉力的自由握持和静态握持任务。每个任务都使用了多种抓握方式以及两种不同的物体涂层，这两种涂层会在手部与手持物体之间产生不同的摩擦力。两项任务均显示，随着摩擦力增加，相对安全裕度增加，而绝对安全裕度要么保持不变（自由握持），要么呈现适度的负相关关系（静态握持任务）。自由握持时的相对安全裕度和绝对安全裕度也均高于静态握持。后一结果可能是任务机械条件（即动态与静态）所致，而非神经控制机制差异（分别为反馈与前馈）所致。所得结果表明，在未来针对健康人群和临床人群的手部力量协调研究中应使用绝对安全裕度（而非相对安全裕度），同时应分别评估从静态和动态操作任务中获得的握力适应性。
