Factors affecting grip force: anatomy, mechanics, and referent configurations.

Satyajit Ambike, Florent Paclet, Vladimir M. Zatsiorsky, Mark L. Latash
Exp Brain Res. 2014-01-31; 232(4): 1219-1231
DOI: 10.1007/s00221-014-3838-8

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1. Exp Brain Res. 2014 Apr;232(4):1219-31. doi: 10.1007/s00221-014-3838-8. Epub 2014
Jan 31.

Factors affecting grip force: anatomy, mechanics, and referent configurations.

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

Author information:
(1)Department of Kinesiology, 39 Rec. Hall, The Pennsylvania State University,
University Park, PA, 16802, USA, .

The extrinsic digit muscles naturally couple wrist action and grip force in
prehensile tasks. We explored the effects of wrist position on the steady-state
grip force and grip-force change during imposed changes in the grip aperture
[apparent stiffness (AS)]. Subjects held an instrumented handle steady using a
prismatic five-digit grip. The grip aperture was changed slowly, while the
subjects were instructed not to react voluntarily to these changes. An increase
in the aperture resulted in an increase in grip force, and its contraction
resulted in a proportional drop in grip force. The AS values (between 4 and 6
N/cm) were consistent across a wide range of wrist positions. These values were
larger when the subjects performed the task with eyes open as compared to
eyes-closed trials. They were also larger for trials that started from a larger
initial aperture. After a sequence of aperture increase and decrease to the
initial width, grip force dropped by about 25% without the subjects being aware
of this. We interpret the findings within the referent configuration hypothesis
of grip-force production. The results support the idea of back-coupling between
the referent and actual digit coordinates. According to this idea, the central
nervous system defines referent coordinates for the digit tips, and the
difference between the referent and actual coordinates leads to force production.
If actual coordinates are not allowed to move to referent ones, referent
coordinates show a relatively slow drift toward the actual ones.

DOI: 10.1007/s00221-014-3838-8
PMCID: PMC4013148
PMID: 24477762 [Indexed for MEDLINE]

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