Startle response and muscular fatigue effects upon fractionated hand grip reaction time

The fractionation of a simple right-hand grip total reaction time (RT) into central and peripheral temporal components (premotor and motor time, respectively) helped to define the site of RT change following an auditory induced startle response and two fatiguing hand-grip exercise regiments for eight males and eight females. Following the startle response, mean values for RT significantly lengthened, due primarily to an increase in premotor time. In contrast, lengthened RT following both fatigue regimens (42% and 55% strength decrements) were due to substantial increases in the motor time component. These results suggest that although performance of tasks which demand a high degree of precision, accuracy, and fine motor control may be disrupted by the introduction of such stressors as an induced startle and local muscular fatigue, the neuromuscular mechanisms mediating performance disruption are dissimilar.