[Purpose] The purpose of this study was to investigate the effect of the use of smartphones on the upper extremity and determine whether there were differences in these changes between smartphone and computer use. [Subject] Forty healthy young adults (18 male, 25 female) took part in this study. [Methods] The pressure pain threshold measurement was assessed at the center of the upper trapezius of the dominant upper limb of the subjects. Electrodes were attached to the subjects in the two experiment groups, who then continuously performed a typing task on their own personal smartphone or computer keyboard for ten minutes. [Results] Regarding the pressure pain threshold of the upper trapezius, the smartphone and computer use groups showed significant decreases after performing the task compared with before it. Regarding muscle fatigue in the four monitored muscles, the smartphone and computer use groups showed deceases in median frequencies in all muscles measured after performing the tasks. The smartphone use group showed statistically significant differences in the brachioradialis, and the computer use group showed statistically significant differences in the upper trapezius when compared with the control group (p <0.05). [Conclusion] We found feasible relationships between smartphone use and musculoskeletal symptoms of the upper extremity and neck and identified physical differences between the smartphone use and computer use.