The aim of this study was to evaluate thumb postures, thumb movements and muscle activity when using mobile phones for SMS messaging and to determine whether there were differences in these exposures (a) across various mobile phone tasks, (b) between gender and (c) between subjects with and with-out musculoskeletal symptoms in shoulders and upper extremities.
Fifty-six young adults (15 healthy
and 41 with musculoskeletal symptoms) performed a series of distinct tasks on a mobile phone. Muscular
load in four forearm/hand muscles in the right arm and the right and left trapezius muscles were mea-
sured using electromyography (EMG). Thumb movements were registered using an electrogoniometer.
The results showed that postures (sitting or standing) and the type of mobile phone task (holding the
phone versus texting) affected muscle activity and thumb positions. Females compared to males had
higher muscle activity in the extensor digitorum and the abductor pollicis longus when entering SMS
messages and tended to have greater thumb abduction, higher thumb movement velocities and fewer
pauses in the thumb movements. Subjects with symptoms had lower muscle activity levels in the abduc-
tor pollicis longus and tended to have higher thumb movement velocities and fewer pauses in the thumb
movements compared to those without symptoms