Forearm EMG response activity during motor performance in individuals prone to increased stress reactivity.

BACKGROUND Work-related Upper Extremity Disorders (WRUEDs) are conceived of as a multifactorial syndrome caused by the effects of excessive repetitive motions, sustained static postures, and muscular stiffness. Our aim is to test an etiological model derived from a theory by Van Galen and Van Huygevoort [2000] Biol Psychol 51:151-171. The theory holds that physical, emotional, and psychosocial stressors enhance muscular stiffness as a compensatory filtering of impoverished signal-to-noise ratios in the motor system. High individual levels of arousal, as measured by Spielberger et al. [1970], State and Trait Anxiety Test would further enhance a subject's predisposition to react with stiffness responses in conditions of stress. METHODS Ten participants with a high- and 10 with a low trait-anxiety score performed a computer task involving series of fast but well-dosed accelerations of the forearm along the surface of a digitizer. To induce cognitive stress a tone had to be remembered simultaneously with the aiming task. Pen-tip displacements and surface electromyographic (EMG) signals were recorded from four forearm muscles. RESULTS Memory load did not affect error rates but produced shorter reaction times and prolonged movement times. EMG data show that under stress overall levels of neuromotor activation were enhanced. High-anxious participants exhibited higher cocontraction levels than low-anxious participants. CONCLUSIONS The findings support the view that stress and muscular tension are closely related and may provide a clue to the origin of WRUEDs.