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1.1 1 xml info:srw/schema/1/mods-v3.2 Friedman Jason author Latash Mark L author Zatsiorsky Vladimir M author 2009 English We examined how the digit forces adjust when a load force acting on a hand-held object continuously varies. The subjects were required to hold the handle still while a linearly increasing and then decreasing force was applied to the handle. The handle was constrained, such that it could only move up and down, and rotate about a horizontal axis. In addition, the moment arm of the thumb tangential force was 1.5 times the moment arm of the virtual finger (VF, an imagined finger with the mechanical action equal to that of the four fingers) force. Unlike the situation when there are equal moment arms, the experimental setup forced the subjects to choose between (a) sharing equally the increase in load force between the thumb and VF but generating a moment of tangential force, which had to be compensated by negatively co-varying the moment due to normal forces, or (b) sharing unequally the load force increase between the thumb and VF but preventing generation of a moment of tangential forces. We found that different subjects tended to use one of these two strategies. These findings suggest that the selection by the CNS of prehension synergies at the VF-thumb level with respect to the moment of force is non-obligatory and reflects individual subject preferences. This unequal sharing of the load by the tangential forces, in contrast to the previously observed equal sharing, suggests that the invariant feature of prehension may be a correlated increase in tangential forces rather than an equal increase. PMID:19554319 exported from refbase (https://refbase.nfshost.com/show.php?record=16), last updated on Mon, 20 Jul 2009 23:44:31 +0000 text http://www.springerlink.com/content/u250552261558533/ https://refbase.nfshost.com/files/friedman/2009/16_Friedman_etal2009.pdf http://www.springerlink.com/content/u250552261558533/ 10.1007/s00221-009-1818-1 19554319 Friedman_etal2009 2009 continuing periodical academic journal 197 1 1 13 1432-1106 1