The purpose of this study was to determine if the changes in selected blood hormones and substrates, metabolic rate, and rectal temperature (Tre) in nine males after immersion in 10 degrees C water, while clad in standard flight suits, were related to the level of aerobic fitness. Fitness was evaluated by the blood lactate response to submaximal exercise. Immersion time (IT) was defined as the time required for a 1 degrees C decrease in Tre and averaged 38.5 (range: 21-62) min. Metabolic rate increased 3.4 times the resting rate. Lactate, free fatty acids, triiodothyronine and thyroxine increased by 81%, 38%, 11%, and 8%, respectively, in contrast to insulin which decreased by 32%, with all changes being statistically significant (p less than 0.05). Glucagon increased slightly but not significantly (p = 0.11) while glucose levels did not change. The IT was correlated directly with a measure of aerobic fitness, with relative body fat, and with the T3 levels postimmersion (p less than 0.05). The results suggest that the aerobic fitness level can significantly influence the cooling rate during water immersion.
"However, Keatinge (1961) found that cold-immersed subjects displayed a reduced metabolic response within the fi rst 30 min of an extended exposure, following endurance training. Others have similarly found that cold-exposed, endurance-trained subjects displayed a reduced thermogenic threshold (Dressendorfer et al. 1977, Kollias et al. 1972), while other investigators have reported improved cold tolerance (Jacobs et al. 1984) and an elevated thermoregulatory sensitivity (Bittel et al. 1988). Notwithstanding these disparate outcomes, it may be argued that endurance training increases metabolic effi ciency during the early stages of cold exposure and, like some cold-adapted ethnic populations, may facilitate enhanced energy conservation during the more stressful stages of exposure. "
Physiological bases of human performance during work and exercise, 1st edited by Nigel Taylor, Herb Groeller, 01/2008: chapter 20: pages 359-377; Churchill Livingstone Elselvier., ISBN: 978 0 443 10271 4
"Young et al. (1989) also found that a substantial reduction in muscle glycogen concentration did not alter the metabolic heat production or body-cooling rate of males immersed in cold water. From these studies it can be concluded, therefore, that even if athletes are severely energy depleted, their ability to retain heat is not lost and they are at no more risk (with respect to temperature regulation) than when they Fig. 2. Relationship between total immersion time required for a 18C decrease in rectal temperature and blood lactate concentration after cycling for 4 min at 200 W. Reproduced with permission from Jacobs et al. (1984). are 'fully fuelled' because of the body's ability to adapt its fuel source. "
[Show abstract][Hide abstract] ABSTRACT: Exercising in the cold is not an attractive option for many athletes; however, defining what represents cold is difficult and is not standard for all events. If the exercise is prolonged and undertaken at a moderate intensity, environmental temperatures around 11 degrees C can be an advantage. If the intensity is lower than this value and the individual does not generate sufficient metabolic heat to offset the effects imposed by the cold environment, then temperatures of 11 degrees C can be detrimental to performance. Similarly, when the performance involves dynamic explosive contractions, then a Cold ambient temperature can have a negative influence. Additional factors such as the exercising medium, air or water, and the anthropometric characteristics of the athlete will also make a difference to the strategies that can be adopted to offset any negative impact of a cold environment on performance. To plan for a performance in the cold requires an understanding of the mechanisms underpinning the physiological response. This review attempts to outline these mechanisms and how they can be manipulated to optimize performance.
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