Influence of Force-Length Relationship and Task-Specific Constraints on Finger Force-Generating Capacities

TL;DR

This study investigates how wrist posture and muscle properties affect finger force capacity, revealing that grip strength loss in certain postures is partly due to the force-length relationship of finger extensors, with task-specific differences.

Contribution

It clarifies the role of the force-length relationship and task-specific constraints in finger force production, using a musculoskeletal model and experimental data.

Findings

Pinch grip force decreases with wrist flexion due to force-length effects.

Press task force remains stable across wrist postures, unaffected by muscle capacity modulation.

Grip strength loss involves mechanical, neural, and muscle length factors.

Abstract

Grip strength loss in extended and flexed wrist postures has been explained by reduced force-generating capacities of extrinsic finger flexor resulting from non-optimal length, owing to the force-length relationship. Recent works suggested that other muscles, especially wrist extensors, participate in this grip strength loss. The objective of this study was to clarify the role of the force-length relationship in finger force production. 18 participants performed maximal isometric finger force production during pinch grip (Pinch) and four-finger pressing (Press) tasks in four different wrist postures (extended, flexed, neutral, spontaneous). The maximum finger force (MFF), finger and wrist joint angles, as well as activation of four muscles were determined using dynamometry, motion capture, and electromyography. The force and length of the four muscles were estimated from joint angles and muscle activation using a musculoskeletal model. MFF decreased for flexed wrist during Pinch but remained stable across wrist postures during Press. The results suggested that the loss of pinch grip force in deviated wrist posture is partially related to force-length relationship of finger extensors. In opposition, MFF during Press was not influenced by the modulation of muscle capacities but was probably first limited by mechanical and neural factors related to finger interdependence