Abstract
The relationship between posture, muscle length properties and performance remains unclear, because of a lack of quantitative data. Studies on grasping tasks suggested that wrist position could favour the extrinsic finger flexor in regards to their length to maximise grip force performance. The present study aimed at providing quantitative evidence of the links between wrist posture, muscle capacities and grip capabilities. It combines experimental measurements and a musculoskeletal model including the force-length relationship of the four prime muscles used in grasping. Participants exerted their maximum grip force on a cylindrical dynamometer in four different wrist postures, including one freely chosen by participants (spontaneous). A musculoskeletal model computed the muscle force level and length from motion capture and muscle activation. Results revealed that participants exerted maximum grip force spontaneously, with a loss of force when using other postures. At muscle force and length level, grip force variation seems to be associated with all the muscles under study. This observation led to a first quantitative link between power grip, posture and muscle properties, which could provide more insight into neuromechanical interaction involved when grasping. The design of ergonomic devices could also benefit from this quantification of the relationship between wrist angle and muscle length properties.
Highlights
The relationship between posture, muscle length properties and performance remains unclear, because of a lack of quantitative data
We hypothesise that (i), maximum grip force will occur for a spontaneous wrist posture in comparison with imposed postures, (ii) the four muscles will be affected differently by wrist postures in terms of force-generating capacities and (iii) the variations of maximum grip force induced by the wrist posture cannot be fully explained solely by the force-generating capacities of extrinsic finger flexors
The influence of wrist posture on grip capabilities and muscle-force generating capacities was evaluated by combining an experimental protocol and a musculoskeletal model of the hand
Summary
The relationship between posture, muscle length properties and performance remains unclear, because of a lack of quantitative data. The specific anatomical configuration of the hand involves strong coupling between the wrist and the finger joints, since several finger muscles, called extrinsic, originate in the forearm and insert via long tendons on distal phalanges During grasping tasks, these muscles are solicited to exert forces on the object and concomitantly create action at the wrist, meaning that gripping actions are inherently linked to the mechanical equilibrium of the wrist[1,2]. A recent study[19] has characterised the in vivo muscle force-generating capacities of representative muscles used for grasping according to the length variations using ultrasound protocols These relationships allow us to explore the influence of joint postures on muscle force-length properties and associate its variations with a performance, here the force level in power grip. We hypothesise that (i), maximum grip force will occur for a spontaneous wrist posture in comparison with imposed postures, (ii) the four muscles will be affected differently by wrist postures in terms of force-generating capacities and (iii) the variations of maximum grip force induced by the wrist posture cannot be fully explained solely by the force-generating capacities of extrinsic finger flexors
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