Evaluation of handle diameters and orientations in a maximum torque task

The effects of gender, handle diameter (25–50 mm), and handle orientation (horizontal and vertical) on the perceived comfort, torque, total finger force, and efficiency of flexor and extensor muscle activity were examined in a maximum torque task. A 16-force sensor glove system was applied to measure finger and phalangeal forces, and a surface EMG was recorded to investigate muscle activities in the torque task. Average maximum torque in the horizontal orientation was about 23.4% more than that in the vertical orientation. The maximum torque was the largest with the 45 and 50 mm diameter handles and least with the 25 mm diameter handle. In both orientations, torque increased as the handle diameter increased, whereas total finger force showed a decreasing pattern which can explain the positive and non-linear correlation between torque output and handle diameter. The efficiency of muscle activity in both orientations followed a similar trend with the torque output for the handle diameters (i.e., the efficiency increased when the handle diameter increased). 35–45 mm handles were rated as the most comfortable for maximum torque exertions. According to a polynomial regression, 37–44 mm and 41–48 mm diameter handles (23.3% of the user's hand length) maximized perceived comfort and were thus recommended for females and males, respectively in this study. This study will provide guidelines for designing better workstations and hand-tools maximizing performance, muscle efficiency, and user's comfort in manual torque tasks.