Effects of armrest height on the neck and shoulder muscle activity in keyboard typing

Use of forearm support during typing is known to alleviate biomechanical stresses on user's neck and upper extremities but it is not known how the change in the armrest height influences the efficiency of the support. The purpose of this study was to investigate the effects of armrest height on the myoelectric activity (EMG) of neck extensors, upper trapezius muscles and forearm muscles during keyboard typing. Twenty-four subjects performed a simple typing task with each of four different armrest conditions (no support, armrests at resting elbow height, armrests at 25% and 40% above resting elbow height) while their EMG amplitudes were periodically collected. Results found significantly greater (p<0.05) mean activity of neck and shoulder muscles associated with elevated armrest heights. Armrest at resting elbow height produced the lowest mean activity. Findings of this study indicate the importance of proper positioning of arm support during typing