Bimanual lifting: response of grip force to perturbations in weight and friction
Date
2017
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Context Being able to live an independent and active life is highly dependent on the ability to manipulate objects and use external supports around us. A body of literature suggests that an elaborate coordination of grip force (GF) and load force (LF) is typically used during successful object manipulation. In the kinetic level, this coordination is measured through several variables including GF scaling, GF-LF coupling, and GF modulation. The tasks are controlled both by a feed-forward and feedback neural mechanism and can be affected by many factors including weight of the object and the friction of the contact surface. The applied GF needs to be high enough to prevent slippage of the object, but low enough to prevent fatigue or crushing of a fragile object. Due to the partly predictive nature of this coordination, unforeseen changes in mechanical conditions can lead to applying inappropriate magnitudes of GF. It has been found that the GF can be affected by different weights and frictions experienced in previous trials in uni-manual tasks. However, it is unknown if the changes in GF are greater when weight or friction is changed. Purpose The purpose of this study is to explore the changes in GF to unforeseen mechanical changes in a bimanual simple task of lifting objects of different weight or friction that induce similar changes in GFmin. The aims of this study were 1) to discern between the effects of friction and weight on applied GF, 2) to observe the differences in changes in GF in the dominant and non-dominant hand, and 3) to explore the changes in GF in the ipsilateral and contralateral hand. Subjects 12 healthy, right handed participants between 18-35 years old who were free of any neurological issues were recruited. Protocol A bimanual simple lifting task using a precision grip was performed. The participants were acclimatized to a standard condition of an object requiring a low GF (LSC) or high GF (HSC) before a change in weight or friction was applied between trials unbeknownst to the participant. The changes imposed were designed to produce similar changes in the required minimum GF regardless of which property was altered. Changes in applied GF were measured during the lifting and holding phase of the movement as well as the rate of GF production. Results The results showed a larger change in applied GF when weight was altered compared to friction of the object in both the LSC ( p<.001) and HSC (p<.001) in both the lifting phase and holding phase. Furthermore, during the holding phase a larger change was seen in the dominant hand compared to the non-dominant hand in the HSC (p=.001). Conclusion The increased changes in applied GF when weight was altered could be due to differences in the spindle and tactile activity associated with the applied interventions. The changes in GF observed in the dominant hand may be in line with the dynamic dominance hypothesis. This information can be applied to future study designs and in the design of objects intended to be manipulated by the hands.
Description
Keywords
Health and environmental sciences, Bimanual lifting, Friction perturbation, Grip force, Lifting task, Weight perturbation