Experimental muscle pain modulates muscle activity and work performance differently during high and low precision use of a computer mouse

The aim was to investigate the influence of experimental muscle pain on per formance and upper extremity muscle activity during occupational work requi ring different levels of precision. Experimental muscle pain was induced by infusing hypertonic saline (0.3 ml, 5% NaCl) into the extensor carpi ulnar is (ECU) muscle. The same amount of isotonic saline was infused on a separa te day to act as a control. Tasks requiring use of a computer mouse with hi gh and low levels of precision were performed during the two sessions. Elec tromyographic (EMG) activity was measured from the ECU, the flexor carpi ra dialis (FCR) and the trapezius muscles. A group of 13 men participated in t he study. Performance measured as work cycle time, cursor movements on the screen, and velocity of cursor movement were unaffected by muscle pain. The ECU muscle pain did not modulate EMG profiles of either the trapezius or F CR muscles - either during high or during low precision work. During the lo w precision work the painful ECU muscle showed lower EMG activity in specif ic phases of the work cycle (highest activity phases) compared to the contr ol session (P < 0.05), whereas during the high precision work, experimental pain had no effect on the activity of the ECU muscle. In conclusion experi mental muscle pain seems to modulate motor control differently depending on the precision level of the task. This may be of importance for our underst anding of why some tasks lead to chronic musculoskeletal disorders.