Tangential load sharing among fingers during prehension.

Area of Science:

• Biomechanics
• Human Factors Engineering
• Motor Control

Background:

• Static prehension involves complex force distribution among digits.
• Understanding finger force sharing is vital for preventing injuries and optimizing tool design.

Purpose of the Study:

• To investigate how loading direction and magnitude affect force sharing during static prehension.
• To analyze the influence of hand posture and digit spacing on grip force distribution.
• To identify key factors influencing tangential force sharing patterns.

Main Methods:

• Utilized a custom-built handle for controlled bi-directional loading (upward/downward) with varying magnitudes (250-1250 g).
• Tested five- and three-digit grasps with different finger spacings (2, 3, 6 cm).
• Analyzed tangential and normal force sharing patterns across different conditions and participant demographics.

Main Results:

• No significant differences in tangential force sharing were observed between males and females.
• Key factors influencing force sharing, ranked by effect size, included trial variability, load magnitude, subject, hand posture, and load direction.
• Normal force sharing explained a substantial portion, but not all, of the tangential force sharing variability.

Conclusions:

• Loading direction is a critical factor to consider in the design of tools requiring functional tangential forces (e.g., screwdrivers, jar lids).
• Passive finger properties may explain observed directional changes in force sharing.
• Further research into the biomechanics of grip force modulation is warranted.