Mechanical properties of the human hand digits

Age-related differences

Jaebum Park, Nemanja Pažin, Jason Friedman, Vladimir M. Zatsiorsky, Mark Latash

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

Background Mechanical properties of human digits may have significant implications for the hand function. We quantified several mechanical characteristics of individual digits in young and older adults. Methods Digit tip friction was measured at several normal force values using a method of induced relative motion between the digit tip and the object surface. A modified quick-release paradigm was used to estimate digit apparent stiffness, damping, and inertial parameters. The subjects grasped a vertical handle instrumented with force/moment sensors using a prismatic grasp with four digits; the handle was fixed to the table. Unexpectedly, one of the sensors yielded leading to a quick displacement of the corresponding digit. A second-order, linear model was used to fit the force/displacement data. Findings Friction of the digit pads was significantly lower in older adults. The apparent stiffness coefficient values were higher while the damping coefficients were lower in older adults leading to lower damping ratio. The damping ratio was above unity for most data in young adults and below unity for older adults. Quick release of a digit led to force changes in other digits of the hand, likely due to inertial hand properties. These phenomena of "mechanical enslaving" were smaller in older adults although no significant difference was found in the inertial parameter in the two groups. Interpretations The decreased friction and damping ratio present challenges for the control of everyday prehensile tasks. They may lead to excessive digit forces and low stability of the grasped object.

Original languageEnglish (US)
Pages (from-to)129-137
Number of pages9
JournalClinical Biomechanics
Volume29
Issue number2
DOIs
StatePublished - Feb 1 2014

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Friction
Hand
Young Adult
Mechanical Phenomena
Hand Strength
Linear Models
Reference Values

All Science Journal Classification (ASJC) codes

  • Orthopedics and Sports Medicine
  • Biophysics

Cite this

Park, Jaebum ; Pažin, Nemanja ; Friedman, Jason ; Zatsiorsky, Vladimir M. ; Latash, Mark. / Mechanical properties of the human hand digits : Age-related differences. In: Clinical Biomechanics. 2014 ; Vol. 29, No. 2. pp. 129-137.
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Mechanical properties of the human hand digits : Age-related differences. / Park, Jaebum; Pažin, Nemanja; Friedman, Jason; Zatsiorsky, Vladimir M.; Latash, Mark.

In: Clinical Biomechanics, Vol. 29, No. 2, 01.02.2014, p. 129-137.

Research output: Contribution to journalArticle

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N2 - Background Mechanical properties of human digits may have significant implications for the hand function. We quantified several mechanical characteristics of individual digits in young and older adults. Methods Digit tip friction was measured at several normal force values using a method of induced relative motion between the digit tip and the object surface. A modified quick-release paradigm was used to estimate digit apparent stiffness, damping, and inertial parameters. The subjects grasped a vertical handle instrumented with force/moment sensors using a prismatic grasp with four digits; the handle was fixed to the table. Unexpectedly, one of the sensors yielded leading to a quick displacement of the corresponding digit. A second-order, linear model was used to fit the force/displacement data. Findings Friction of the digit pads was significantly lower in older adults. The apparent stiffness coefficient values were higher while the damping coefficients were lower in older adults leading to lower damping ratio. The damping ratio was above unity for most data in young adults and below unity for older adults. Quick release of a digit led to force changes in other digits of the hand, likely due to inertial hand properties. These phenomena of "mechanical enslaving" were smaller in older adults although no significant difference was found in the inertial parameter in the two groups. Interpretations The decreased friction and damping ratio present challenges for the control of everyday prehensile tasks. They may lead to excessive digit forces and low stability of the grasped object.

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