Grip-force modulation in multi-finger prehension during wrist flexion and extension

Area of Science:

• Biomechanics
• Neuroscience
• Human Motor Control

Background:

• Extrinsic digit muscles influence both fingertip forces and wrist movements.
• Finger forces are expected to be dependent on wrist position and motion.

Purpose of the Study:

• To investigate the relationship between grip force and wrist kinematics.
• To determine how grip force scales with wrist flexion-extension (FE) angle.
• To examine if grip force can be predicted from accelerations during FE movement.

Main Methods:

• Subjects performed slow and cyclic wrist FE movements while holding an instrumented handle.
• Grip force and wrist kinematics were recorded during these movements.
• A linear regression model was used to analyze the relationship between forces and accelerations.

Main Results:

• Grip force remained constant across most wrist positions in quasistatic conditions.
• During cyclic movements, grip force changes were accurately predicted (99% variability explained) by a model incorporating tangential and radial accelerations and object weight.
• Grip force independence from wrist position supports a two-variable neural control theory for digit forces.

Conclusions:

• Grip force is primarily influenced by accelerations rather than static wrist position.
• Findings support the principle of superposition in motor control, where complex actions are composed of simpler, independently controlled elements.
• The study advances the understanding of neural control mechanisms for hand forces during combined grip and wrist movements.