Optimal cylindrical handle diameter for grip force tasks

This study tested maximum grip force on cylindrical aluminum handles to evaluate the relationships between handle diameter (25–50 mm diameter handles), perceived comfort, finger and phalange force distribution, and electromyographic efficiency of finger flexor and extensor muscle activity. A force glove system containing 16 thin profile force sensors was developed to measure finger and phalangeal forces on the cylindrical handles. Participants (n=24) rated the mid-sized handles (30, 35 and 40 mm) as the most comfortable for maximum grip force exertions. Using a polynomial regression the handle diameter that maximized subjective comfort was calculated as a function of the user's hand length. This optimal handle diameter was 19.7% of the user's hand length. Total finger force capability was inversely related with handle diameter. Electromyographic amplitude of the primary flexor and extensor was unaffected by handle diameter, so the efficiency of the muscle electrical activity followed the same relationship with handle diameter as total finger force. Individual finger and phalange force distributions were examined to evaluate their relationship with perceived comfort. A non-uniform finger/phalange force distribution, in which finger force was proportional to finger muscle capabilities, exhibited a stronger correlation with subjective ratings of comfort than a uniform finger/phalange force distribution. Results obtained in this study will provide guidelines to hand-tool designers and manufacturers for maximizing handle comfort based on the user's hand size.