Frictional properties of different hand skin areas and grasping techniques

Abstract

High friction is crucially important in manipulation activities for reducing the hand grip forces and improving control of manipulative tasks. The aim of this study was to assess the coefficient of friction (COF) of various areas of hand skin. Static COF of nine different grasping techniques applied against two object coatings was assessed by means of the ‘slip point’ method in 16 participants. COF measures proved to be both highly reliable and considerably variable across participants (coefficients of variation ranging from 25 to 75%, depending on the applied grasp). COF was also higher in ‘specialised’ than in ‘non-specialised’ skin areas for grasping, as well as in palms, than in the tips of the fingers. The observed findings are of importance for optimisation of object manipulations and also emphasise the importance of measuring individual COF in ergonomic, biomechanics and motor control studies.

Statement of Relevance:The results reveal prominent differences in skin friction not only across various areas of the hand, but also across participants. While the former finding is relevant for optimisation of manipulation activities, the latter emphasises the importance of assessment of individual COF in studies of hand function.

Keywords:

• coefficient of friction
• force
• grip
• manipulation

Acknowledgement

The study was supported in part by a grant from the Serbian Research Fund (#145 082) to S. Jaric. P.B. de Freitas has been partly supported by the Fulbright Program (#15053184) and Brazilian Government (Coordination for Improvement of Higher Education Personnel – CAPES #2051–04/4).