The influence of stress-induced muscle effort during computer utilization was tested in patients with repetitive strain injury (RSI). Twenty academic researchers with a formal medical diagnosis of RSI and 20 matched controls, randomly selected from a sample of 71 colleagues with and without RSI, typed after stress (induced via an intelligence/skill task under social pressure) and after relaxation. Results indicated that both groups had more electromyography (EMG) activity in the shoulder muscles during typing after stress than after relaxation, but that patients started with higher baseline muscle activity. Furthermore, EMG activity of different muscle groups during typing after stress correlated among controls, but not among patients. Finally, analysis of intake forms showed that patients scored higher than controls on neuroticism and alexithymia, but not on extraversion, openness, agreeableness and conscientiousness. It was concluded that deviations in muscle activity during computer utilization, as well as neuroticism and alexithymia, may be risk factors for RSI.