Psychomotor deterioration during exposure to heat

The effect of different heat loads on vigilance and complex cognitive tasks involved in a mission of different intensities were examined. Nine healthy volunteers were randomly exposed for 2hr to three climatic conditions: comfort (21°C ET), moderate heat load (30°C ET) and severe heat load (35°C ET). The subjects were assigned to missions of shooting at targets of three different sizes. Physiological parameters (HR, T(re), and sweat rate) and psychomotor ability were monitored. Exposure to 35°C ET gave rise to elevated HR, T(re), and dehydration of 2.5%, while exposure to 21°C and 30°C ET caused no physiological burden. Speed of performance was significantly higher when the subjects were exposed to moderate heat load than to either comfort or severe heat load. Percentage of errors, however, rose gradually with the rise in heat load. The results indicate: The effect of the intensity of the task and heat load on deteriorating performance are synergistic; psychomotor performance deteriorates even before physiological parameters are impaired, possibly because of feelings of discomfort; and even highly motivated subjects are effected by heat load, especially when assigned to complex missions which require a high state of vigilance, cooperation, and coordination.