Pain induced by a single simulated office-work session: time course and association with muscle blood flux and muscle activity

Abstract

The present study aimed to assess the development of pain during computer work with high precision demand and time pressure, and the association between pain and muscle blood fluxes and muscle activity. Twenty-eight healthy subjects (range 22-44 years) performed a 90-min standardized task of correcting a text on a word-processor. Monetary reward was given according to productivity in order to induce time pressure. Pain intensity, general tension, and eye strain were reported on visual analogue scales before, during and after the computer session. Intramuscular trapezius blood fluxes were recorded by laser-Doppler flowmetry (LDF) and analyzed as % of baseline level. Muscle activity was measured from the upper trapezius and forearm extensors by surface electromyography (EMG), analyzed as % of a maximal calibration contraction, %EMG(max). Pain, tension, and eye strain increased considerably during the computer session with different time course for pain and tension. The LDF of the active side of trapezius was elevated for 30 min followed by a falling trend. There was an initial short-lasting increase in the inactive trapezius. The upper trapezius EMG was low (<3 % of EMG(max)) but increased during the work, similar in both the active and passive side. There was a significant time and blood flux interaction effect on pain in the shoulders/neck, but no association with EMG. In conclusion, considerable neck/shoulder pain may develop in healthy pain-free subjects during 90 min of office-work and seems to be related to the regulation of trapezius muscle blood flow.