The Effect Of Selective Head-cooling On Performance And Energy And Fatigue After 4o Minutes Of Aerobic Cycling Exercise In The Heat.

Abstract

PURPOSE: Determining the factors that limit endurance performance has received considerable attention. Secher and Amman propose that afferent feedback from the fatigued skeletal muscle is the primary determinant of endurance performance. By contrast, Marcora proposes a psychobiological model in which factors such as the perception of effort are principal. Developing methods to distinguish the effect of peripheral vs. central factors would provide insight into this debate. Selectively cooling the head during exercise is one way to potentially provide disparate signals from the brain and the periphery. Therefore, the effects of head cooling on exercise performance in the heat were evaluated in this study. METHODS: Twenty-two young, non-obese (BMI=23.8 kg/m2) men between the ages of 18 and 23 years participated in the study (19.8 +/-1.6 yr). Baseline VO2 peak testing in the heat (35.0 +/- 0.1°C) was followed by a counter-balanced repeated measures design in which participants cycled in the heat (35.0 +/- 0.3°C) for 40 minutes at 65% relative VO2 peak. After 40 minutes of aerobic exercise, participants rested for seven minutes with head cooling (or sham cooling) then performed a final VO2 peak test. Profile of Mood States (POMS) and tympanic temperature were recorded four times: before and after the 40-minute bout of aerobic exercise, as well as before and after the final VO2 peak test. In addition, peak power, VO2, lactate, RPE, and HR were recorded during and at the end of each VO2 peak test. RESULTS: Head-cooling significantly attenuated the heat-induced reduction in power by 50% (-11.8 +/- 19.9 watts) when compared to sham (-24.3 +/- 23.3 watts) (p = 0.002) which translated to a time to exhaustion that was 32 seconds longer after head cooling compared to sham. By contrast, there was no difference between cool-cap and sham for core body temperature (p = 0.91; 38.3 0.3 and 38.7 0.4, respectively), tympanic temperature (p = 0.68, 0.17 +/- 0.44 and 0.22 +/- 0.48), or changes in energy (p=0.864; 0.18 +/-4.91) and fatigue (p=0.54; 0.45 +/- 3.4) as measured by the POMS. DISCUSSION: Our initial results suggest that neither peripheral nor central signals significantly contributed to the increased performance that resulted from head cooling. Future studies could evaluate alterations to efficiency or utilize other measures of energy and fatigue.