A Study of One-handed Interaction of Large Smartphones: GUI Changes for Better Ergonomics
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- Institutt for design 
People tend to use their smartphones one-handed, which is unergonomic for the human musculoskeletal system. Stretching the thumb to reach certain touch keys is uncomfortable. Especially now that smartphones have large screens, normally ranging from 4.5” and above. Exaggerated use of smartphones can lead to repetitive strain injury (RSI), which is caused by static, repetitive movements over an extended time. This master thesis investigates how different touch key locations and touch key sizes affect the ergonomics of user interfaces on large smartphones. Moreover, it examines if the principles of the functional area improve the ergonomics of mobile user interfaces. The functional area is the surface of the touchscreen that is reachable by the thumb. Expert interviews were used to collect data to make hypotheses regarding improving the ergonomics of mobile user interfaces for one-handed interaction. An electromyography (EMG) test was conducted to investigate the hypotheses. EMG is a technology used to measure muscle contractions. The results show a significant correlation between a user interface that applies the functional area and a decline in muscle contraction. However, the decline in muscle contraction only occurs if the functional area is designed specifically for the user’s dominant hand. There were no significant differences between the touch key sizes and the extent of muscle contraction. The findings from this master thesis support the idea that the functional area and changes in the user interface design affect the ergonomics of smartphone interaction.