TY - JOUR
T1 - Factors affecting grip force
T2 - Anatomy, mechanics, and referent configurations
AU - Ambike, Satyajit
AU - Paclet, Florent
AU - Zatsiorsky, Vladimir M.
AU - Latash, Mark L.
N1 - Funding Information:
the first hypothesis formulated in the “Introduction”— grip as would vary with wrist position—received partial support. While as varied, this variation was limited to postures in a close proximity to the fully flexed wrist position. this observation is consistent with our earlier study (ambike et al. 2013), wherein the “natural grip force” for the extreme wrist flexion was higher than for all other wrist positions. Other wrist positions had no effect on as, so for those positions, hypothesis-1 is rejected by the data. hypothesis-2—as increases with initial aperture size— is supported by the data. the larger initial grip aperture
PY - 2014/4
Y1 - 2014/4
N2 - 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.
AB - 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.
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U2 - 10.1007/s00221-014-3838-8
DO - 10.1007/s00221-014-3838-8
M3 - Article
C2 - 24477762
AN - SCOPUS:84897023836
VL - 232
SP - 1219
EP - 1231
JO - Experimental Brain Research
JF - Experimental Brain Research
SN - 0014-4819
IS - 4
ER -