The influence of cold stress and a 36- h fast on the physiological responses to prolonged intermittent walking in man

In a previous study, rectal temperature (Tre) was found to be lower, and oxygen consumption (VO2) and the respiratory exchange ratio (R) were higher in a cold (+5 degrees C), wet and windy environment (COLD), compared with a thermoneutral environment during intermittent walking at approximately 30% of peak VO2 (Weller AS, Millard CE, Stroud MA et al. Am J Physiol 272:R226-R233, 1997). The aim of the present study was to establish whether these cold-induced responses are influenced by prior fasting, as impaired thermoregulation has been demonstrated in cold-exposed, resting men following a 48-h fast. To address this question, eight men attempted a 360-min intermittent (15 min rest, 45 min exercise) walking protocol under COLD conditions on two occasions. In one condition, the subjects started the exercise protocol approximately 120 min after a standard meal (FED/ COLD), whereas in the other the subjects had fasted for 36 h (FASTED/COLD). The first two exercise periods were conducted at a higher intensity (HIGHER, 6 km x h[-1] and 10% incline), than the four subsequent exercise periods (LOW, 5 km x h[-1] and 0% incline). There was no difference in the time endured in FED/ COLD and FASTED/COLD. In FASTED/COLD compared with FED/COLD, R was lower during HIGHER and LOW, and Tre was lower during LOW, whereas there was no difference in VO2, mean skin temperature and heart rate. Therefore, although the 36-h fast impaired temperature regulation during intermittent low-intensity exercise in the cold, wet and windy environment, it was unlikely to have been the principal factor limiting exercise performance under these experimental conditions.