Grip-force modulation in multi-finger prehension during wrist flexion and extension.

Satyajit S. Ambike, Florent Paclet, Mark L. Latash, Vladimir M. Zatsiorsky
Exp Brain Res. 2013-04-30; 227(4): 509-522
DOI: 10.1007/s00221-013-3527-z

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1. Exp Brain Res. 2013 Jun;227(4):509-22. doi: 10.1007/s00221-013-3527-z. Epub 2013
Apr 30.

Grip-force modulation in multi-finger prehension during wrist flexion and

Ambike SS(1), Paclet F, Latash ML, Zatsiorsky VM.

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Extrinsic digit muscles contribute to both fingertip forces and wrist movements
(FDP and FPL-flexion, EDC-extension). Hence, it is expected that finger forces
depend on the wrist movement and position. We investigated the relation between
grip force and wrist kinematics to examine whether and how the force (1) scales
with wrist flexion-extension (FE) angle and (2) can be predicted from
accelerations induced during FE movement. In one experiment, subjects naturally
held an instrumented handle using a prismatic grasp and performed very slow FE
movements. In another experiment, the same movement was performed cyclically at
three prescribed frequencies. In quasistatic conditions, the grip force remained
constant over the majority of the wrist range of motion. During the cyclic
movements, the grip force changed. The changes were described with a linear
regression model that represents the thumb and virtual finger (VF = four fingers
combined) normal forces as the sum of the effects of the object’s tangential and
radial accelerations and an object-weight-dependent constant term. The model
explained 99 % of the variability in the data. The independence of the grip force
from wrist position agrees with the theory that the thumb and VF forces are
controlled with two neural variables that encode referent coordinates for each
digit while accounting for changes in the position dependence of muscle forces,
rather than a single neural variable like referent aperture. The results of the
cyclical movement study extend the principle of superposition (some complex
actions can be decomposed into independently controlled elemental actions) for a
motor task involving simultaneous grip-force exertion and wrist motion with
significant length changes of the grip-force-producing muscles.

DOI: 10.1007/s00221-013-3527-z
PMCID: PMC3766344
PMID: 23625077 [Indexed for MEDLINE]

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