Almost 50% of the subjects owned or had owned that specific model or a similar, older model made by Nokia. Most of the other subjects had experience with the phone model through friends or siblings.
The first task they performed was making a phone call with the standard mobile phone and then talking on the phone for four minutes (A). This task acted as a reference task since talking required gripping the phone (as during text messaging) but not pressing the keys (the factor we were interested in studying). Then, the subjects performed three different SMS tasks with the standard phone: entering a 300 character standardized SMS message from a piece of paper while sitting (B), composing and entering their “own” 300 character SMS message while sitting (C) and composing and entering their “own” 300 character SMS message while standing (D). The experiment concluded with subjects composing and entering their own 300 character SMS message on their own personal mobile phone while sitting (E). During the standardized SMS task (B) the subjects were instructed to turn off and not use the automatic word completion function, which required that they had to text every character. During their “own” SMS tasks (C–E) they were instructed to write and use the functions they normally did when entering an ordinary SMS message. The order of the four SMS tasks (B–E) was randomised for each subject and the time it took subjects to enter each message was measured.
The standardized SMS message task (B) was performed by all 56 subjects and 24 of the 56 subjects performed all tasks (A–E).
The subjects were instructed to sit and stand using the same positions and working techniques that matched how they used their mobile phones in real life. The chair used in sitting tasks had a backrest, and armrests and no wheels. The subjects‘ hand size (width and length) was measured according to Pheasant (Pheasant, 1986) and a video documentation was made of the subjects’ posture during every task.
The muscular load in six muscles in the right forearm/hand and both shoulders were registered by electromyography (EMG) and thumb position and movements in the right thumb were registered by an electrogoniometer during each task.