Prehension synergies: A study of digit force adjustments to the continuously varied load force exerted on a partially constrained hand-held object

Jason Friedman, Mark Latash, Vladimir M. Zatsiorsky

Research output: Contribution to journalArticle

Abstract

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.

Original languageEnglish (US)
Pages (from-to)1-13
Number of pages13
JournalExperimental Brain Research
Volume197
Issue number1
DOIs
StatePublished - Jul 1 2009

Fingerprint

Thumb
Hand
Fingers

All Science Journal Classification (ASJC) codes

  • Neuroscience(all)

Cite this

@article{5690e520d635446c9293e44333106d1e,
title = "Prehension synergies: A study of digit force adjustments to the continuously varied load force exerted on a partially constrained hand-held object",
abstract = "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.",
author = "Jason Friedman and Mark Latash and Zatsiorsky, {Vladimir M.}",
year = "2009",
month = "7",
day = "1",
doi = "10.1007/s00221-009-1818-1",
language = "English (US)",
volume = "197",
pages = "1--13",
journal = "Experimental Brain Research",
issn = "0014-4819",
publisher = "Springer Verlag",
number = "1",

}

Prehension synergies : A study of digit force adjustments to the continuously varied load force exerted on a partially constrained hand-held object. / Friedman, Jason; Latash, Mark; Zatsiorsky, Vladimir M.

In: Experimental Brain Research, Vol. 197, No. 1, 01.07.2009, p. 1-13.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Prehension synergies

T2 - A study of digit force adjustments to the continuously varied load force exerted on a partially constrained hand-held object

AU - Friedman, Jason

AU - Latash, Mark

AU - Zatsiorsky, Vladimir M.

PY - 2009/7/1

Y1 - 2009/7/1

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=67549089999&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=67549089999&partnerID=8YFLogxK

U2 - 10.1007/s00221-009-1818-1

DO - 10.1007/s00221-009-1818-1

M3 - Article

C2 - 19554319

AN - SCOPUS:67549089999

VL - 197

SP - 1

EP - 13

JO - Experimental Brain Research

JF - Experimental Brain Research

SN - 0014-4819

IS - 1

ER -