Motor redundancy during maximal voluntary contraction in four-finger tasks

Area of Science:

• Biomechanics
• Human Motor Control
• Ergonomics

Background:

• Understanding force distribution among fingers is crucial for analyzing hand function and designing ergonomic tools.
• Previous research has explored single-finger force capabilities, but multi-finger force sharing remains less understood.

Purpose of the Study:

• To investigate force-sharing patterns in multi-finger tasks.
• To determine how thumb position influences normal and shear forces exerted by individual fingers.
• To analyze the relationship between finger force distribution and hand stability.

Main Methods:

• Measured maximal normal force (MNF) and force-time curves of individual fingers in 10 young males.
• Utilized three tasks: static grip with thumb at varied positions, preferred thumb grip, and a pressing task.
• Analyzed force moments, shear forces, and force-force relationships among fingers.

Main Results:

• A neutral thumb position was identified where the net force moment and shear force were zero.
• Maximal total normal force peaked at the preferred comfortable thumb position.
• Force-sharing patterns were more linear and stable at comfortable thumb positions, with significant correlations between index and little finger forces.
• Individual finger peak forces in multi-finger tasks were substantially lower than in single-finger tasks, ranging from 11.3% to 65.2%.

Conclusions:

• The hand dynamically adjusts force sharing among fingers to minimize moments around the functional hand axis.
• Thumb position significantly influences force distribution and stability during grip and pressing tasks.
• Optimal thumb placement, identified as the comfortable position, leads to more predictable and stable force-sharing strategies.