Body temperature related factors diminishing the drive to exercise

Abstract

The effects of slightly below-normal body temperatures (ΔTcore –0.5 to 1 °C) on exercise performance were examined in four series of studies employing a standardized precooling maneuver. In both the precooling tests and the control tests the subjects exercised on a cycle ergometer at an ambient temperature of 18 °C with the following results. In series 1, the subjects were exercising at a heart rate of 120 beats∙min−1. Work rate and oxygen pulse were significantly increased, and sweat rate was less elevated in precooling tests than in controls. In series 2, in 12 well-trained rowers subjected to an incremental performance test, maximum work rate, peak [Formula: see text], time to exhaustion, and total work were not reduced in precooling tests. Eight well-trained rowers in series 3 were requested to work as hard as possible for 1 h. The mean work rate, [Formula: see text], and oxygen pulse were increased in the precooling tests by 6.8, 9.6, and 5.6%, respectively, whereas the sweat rate was 20% lower. In series 4 after a 16-min period of easy exercise (phase 1) the subjects exercised at a work rate corresponding to 80% [Formula: see text] up to exhaustion. Endurance time at this work rate was increased in precooling tests by 12% (18.5 vs. 20.8 min, p = 0.035). Heart rate was lower throughout the exercise period in precooling tests. Oxygen pulse, as well as stroke volume and arteriovenous oxygen difference (AVDo2), measured by impedance cardiography were increased in phase 1; during min 16–28 (phase 2) precooled–control differences in stroke volume and AVDo2 disappeared, but pedal rate (which is related to muscle force, muscle metabolism efficiency, and fatigue) was significantly reduced in precooling tests. Sweat rate and skin blood flow increased less in phase 2 of the precooling test. In conclusion, changes in circulatory, thermoregulatory, and muscular factors have been demonstrated after precooling. These may account for a smaller increase in exercise discomfort counteracting the drive to exercise.