HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 98/1/16    most recent 00058.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Niu, X. Articles by Zatsiorsky, V. M. Search for Related Content PubMed PubMed Citation Articles by Niu, X. Articles by Zatsiorsky, V. M.

Prehension Synergies in the Grasps With Complex Friction Patterns: Local Versus Synergic Effects and the Template Control

Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania

Submitted 17 January 2007; accepted in final form 5 May 2007

We studied adjustments of digit forces to changes in the friction. The subjects held a handle statically in a three-digit grasp. The friction under each digit was either high or low, resulting in eight three-element friction sets (such grasps were coined the grasps with complex friction pattern). The total load was also manipulated. It was found that digit forces were adjusted not only to the supported load and local friction, but also to friction at other digits (synergic effects). When friction under a digit was low, its tangential force decreased and the normal force increased (local effects). The synergic effects were directed to maintain the equilibrium of the handle. The relation between the individual digit forces and loads agreed with the triple-product model: f_iⁿ = k_i⁽²⁾k_i⁽¹⁾L, where f_iⁿ is normal force of digit i, L is the load (newtons), k_i⁽¹⁾ is a dimensionless coefficient representing sharing the total tangential force among the digits ( k_i⁽¹⁾ = 1.0), and k_i⁽²⁾ is a coefficient representing the relation between the tangential and normal forces of digit i (the overall friction equivalent, OFE). At each friction set, the central controller selected the grasping template—a three-element array of k_i⁽²⁾k_i⁽¹⁾ products—and then scaled the template with the load magnitude.