A study on the relationships among hand muscles and form factors of large-screen curved mobile devices

The aim of this study is to determine the effect of form factors (curvature rate, depth) of mobile devices on hand comfort when using large-screen curved mobile devices. To that end, four muscles (APB, APL, FDI, EDC) were selected and mockups for experiment were developed with four curvature rate levels (flat/100/200/300R) and five depth levels (3/5/7/9/11 mm). User experiment was conducted using three interactions (tapping, dragging, and texting) that usually take place on smartphones. EMG signal of each participant was measured. Combination of curvature and depth could maximize the physical comfort of hands and fingers through the experiment so that the interaction effect between form factors and tasks could be identified. Our results revealed that only APL and FDI had statistically significant muscle activity amounts across the curvature rates. With respect to effect of depth, all four muscles showed statistically significant difference in muscle activity. Moreover, results from the interaction effect among task levels of two tasks (target location of tapping and direction of dragging) and two form factors showed no interaction effect in either tapping or texting. The results of this study could be used to determine the optimal range for form factors of curved screen mobile devices in terms of physical comfort of the hand while using large-screen devices.