External finger forces in submaximal five-finger static pinch prehension

Area of Science:

• Biomechanics
• Human Motor Control
• Ergonomics

Background:

• Understanding individual finger contributions to pinch force is crucial for assessing hand function and designing ergonomic tools.
• Previous research has often focused on overall pinch strength rather than the distribution of force among individual fingers.

Purpose of the Study:

• To quantify individual finger forces during submaximal static pinch tasks.
• To investigate how force distribution changes with varying exertion levels and external loads.
• To determine the relative contribution of each finger to total pinch force.

Main Methods:

• Small conductive polymer force sensors were attached to distal phalangeal pads to measure individual finger forces.
• A strain gauge dynamometer measured resultant five-finger pinch force during tasks with fixed total force levels (10-30% MVC) and fixed external loads (1.0-2.0 kg).
• Measurements were taken at two pinch spans (45 mm and 65 mm) with a neutral wrist posture.

Main Results:

• The index and middle fingers consistently exerted greater average force than the ring and small fingers.
• At 30% maximum voluntary exertion, index and middle fingers exerted over 5 N more force than ring and small fingers.
• Finger force contributions varied with exertion level; middle finger contribution increased from 25% to 38% as exertion rose from 10% to 30%.

Conclusions:

• Individual finger force modulation is significant during static pinch, with the index and middle fingers playing a dominant role.
• The distribution of force among fingers is not uniform and is influenced by the required exertion level.
• These findings have implications for understanding hand function, rehabilitation, and the design of grips and tools.