Evaluation of Various Handle Grip Spans for Optimizing Finger Specific Force Based on the Users' Hand Sizes

This study evaluated the effects of handle grip span and user's hand size on maximum grip strength and individual finger force using a computerized digital dynamometer with five various grip spans (45, 50, 55, 60, and 65mm). Forty-six males participated and were assigned into three hand size groups (small, middle, large) according to their hand lengths. Results showed that generally 55 and 50mm grip spans had the highest grip strength (433.6N and 430.8N, respectively), whereas 65mm grip span had the least grip strength. With respect to the interaction effect of grip span and hand size, small hand sized participants produced the highest grip forces at the 45mm grip span, followed by 50 and 55mm, middle hand size participants provided the highest grip force at the 55mm followed by 50 and 45mm, whereas large hand size participants exerted the highest grip force at the 55mm followed by 60mm. In the analysis of individual finger force, the middle finger force was the strongest and the highest contribution (37.5%) to the total finger force, followed by ring (28.7%), index (20.2%) and little (13.6%) fingers. In addition, it was noted that each finger had a different optimal grip span for exerting maximum force, resulting in a bowed contoured shaped handle (i.e., the grip span of the handle at the center is larger than that of the handle at the end) for two-handle hand tools.