Comparison of the influence of two stressors on steadiness during index finger abduction.

Although several stressors have been used to examine the influence of arousal on motor performance, including noxious electrical stimulation, cold pressor test, and mental math calculations, no study has compared the influence of different physical stressors on motor output. The purpose of the study was to compare the influence of two stressors (cold pressor test and electrical stimulation) on the steadiness of the abduction force exerted by the index finger. Sixteen subjects (22.8+/-3.5 years, 8 women) performed steadiness trials before (anticipatory phase), during (stressor phase), and after (recovery phase) each stressor. The steadiness task involved isometric contractions with the first dorsal interosseus muscle, which is the muscle that produces most of the abduction force exerted by the index finger. Subjects were required to match the abduction force on a monitor to a target force set to 5% of the maximal voluntary contraction (MVC) force for 60s. In contrast to previous studies that examined the influence of stressors on pinch grip steadiness, the two stressors did not decrease steadiness. Furthermore, the absence of a change in steadiness contrasted with the increases in cognitive (State-Trait Anxiety Index, Visual Analog Scale) and physiological (heart rate) arousal during the stressor phase and the subsequent decline during recovery. The null effect of the stressors on index finger steadiness may be due to the relative simplicity of the task compared with those examined previously.