Handle grip span for optimising finger-specific force capability as a function of hand size.

Area of Science:

• Ergonomics and Human Factors
• Biomechanics
• Industrial Design

Background:

• Grip span significantly influences grip strength, comfort, and tool performance.
• Understanding the interplay between user hand size and handle grip span is crucial for ergonomic tool design.
• Existing hand tool designs may not optimally accommodate diverse user anthropometrics.

Purpose of the Study:

• To evaluate the effects of handle grip span and user hand size on maximum grip strength, individual finger force, and comfort.
• To determine optimal grip spans for maximizing grip strength and subjective comfort across different hand sizes.
• To provide design guidelines for two-handle hand tools based on anthropometric data.

Main Methods:

• Utilized a computerized digital dynamometer with independent finger force sensors to measure grip strength and forces.
• Tested five grip spans (45-65 mm) with 46 male participants categorized into small, medium, and large hand size groups.
• Calculated normalized grip span (NGS) ratios to correlate hand length with optimal handle grip span.

Main Results:

• The 50-mm and 55-mm grip spans yielded the highest grip strength and comfort ratings.
• Optimal grip span varied by hand size; small/medium hands preferred 50-55 mm, while large hands preferred 55-60 mm.
• The middle finger contributed most to grip force (37.5%), indicating varied optimal spans for individual fingers and suggesting bow-contoured handles.

Conclusions:

• Grip span and hand size are critical factors for maximizing grip strength and user comfort in hand tools.
• Normalized grip span (NGS) ratios can guide the design of tool grip spans tailored to user hand dimensions.
• Findings support the design of two-handle tools with grip spans optimized for user anthropometrics to enhance performance and comfort.