Objectives: This study explores the effects of mental and physical demands on muscular activity in the use of the mouse and keyboard in computer work in a time-pressed situation.
Methods: Twelve female subjects performed a computer task with four combinations of two forms of input device (computer mouse and keyboard) and two levels of mental demand (with and without a color word test). The time available for response was limited. Performance and electromyography (EMG) were recorded for the forearm, shoulder, and neck muscles.
Results: The mean static muscular activity was 2-7% of the maximum EMG for the forearm and neck extensor muscles. All the muscles for which recordings were made showed increased muscular activity in the mentally demanding condition. The increase in the static muscular activity level varied from 0.3% of the maximum EMG for the right trapezius muscle to 2.6% for the extensor carpi ulnaris muscle. Significant differences in muscular activity between the use of a computer mouse and a keyboard were only found for the neck extensors; in the computer mouse condition there was a static EMG level of 3.5% for the maximum EMG, compared with 2.8% for the keyboard.
Conclusions: Mental demands during computer work increased muscular activity in all of the recorded muscles. Increased muscular activity was found in the neck during the use of the mouse in comparison with the use of the keyboard; this phenomenon may be related to higher visual demands during the use of a mouse than with a keyboard. These findings may help explain the adverse effects of psychosocial work factors on the musculoskeletal system.