Relationship Between Operability in Touch Actions and Smartphone Size Based on Muscular Load
The objective of this study was to examine the changes in muscular loads of the forearm/hand areas and in the subjective responses associated with operability and discomfort levels when participants performed touch action on different sizes of smartphones. In the experiment, finger motions and electromyograms (EMGs) of three muscles were recorded during reciprocal tapping tasks with the smartphones while participants were in the seated position. Three sizes of smartphones as well as one with a small soft keyboard for minimizing dynamic thumb motions as an intervention were provided. The data showed that muscular loads on the thumb abduction and flexion of the proximal interphalangeal joints of the finger were affected by the size of the smartphone used. A large smartphone with the keyboard intervention successfully reduced the muscular load for abduction of the thumb and, as a second-order effect, the force for holding the smartphone by using finger flexors. The subjective ratings of difficulty in touch action were significantly affected by the size of smartphone, and the subjective ratings of difficulty in gripping the smartphone were also affected by the size of smartphone. The results implied that both input method for reducing the amount of thumb abduction and key layout for reducing reach by the thumb are recommended to reduce the muscular loads for operating large smartphones.
KeywordsTouch action Smartphone Operability Musculoskeletal disorders
Part of the present study was funded by Advanced-biomedical sensing technology research group Kansai University, and Kakenhi of the Japan Society for the Promotion of Science (26560036). The authors would like to thank Yosuke Sano during the data collection.