Enslaving in a serial chain: interactions between grip force and hand force in isometric tasks.
Exp Brain Res. 2013-12-06; 232(3): 775-787
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1. Exp Brain Res. 2014 Mar;232(3):775-87. doi: 10.1007/s00221-013-3787-7. Epub 2013
Enslaving in a serial chain: interactions between grip force and hand force in
Paclet F(1), Ambike S, Zatsiorsky VM, Latash ML.
(1)Department of Kinesiology, Rec.Hall-268N, The Pennsylvania State University,
University Park, PA, 16802, USA.
This study was motivated by the double action of extrinsic hand muscles that
produce grip force and also contribute to wrist torque. We explored interactions
between grip force and wrist torque in isometric force production tasks. In
particular, we tested a hypothesis that an intentional change in one of the two
kinetic variables would produce an unintentional change in the other (enslaving).
When young healthy subjects produced accurate changes in the grip force, only
minor effects on the force produced by the hand (by wrist flexion/extension
action) were observed. In contrast, a change in the hand force produced
consistent changes in grip force in the same direction. The magnitude of such
unintentional grip force change was stronger for intentional hand force decrease
as compared to hand force increase. These effects increased with the magnitude of
the initial grip force. When the subjects were asked to produce accurate total
force computed as the sum of the hand and grip forces, strong negative
covariation between the two forces was seen across trials interpreted as a
synergy stabilizing the total force. An index of this synergy was higher in the
space of “modes,” hypothetical signals to the two effectors that could be changed
by the controller one at a time. We interpret the complex enslaving effects
(positive force covariation) as conditioned by typical everyday tasks. The
presence of synergic effects (negative, task-specific force covariation) can be
naturally interpreted within the referent configuration hypothesis.
PMID: 24309747 [Indexed for MEDLINE]