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Body temperature manipulation and exercise performance in athletically trained males

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posted on 09.11.2012, 10:26 by Steve H. Faulkner
Exercise or activity in high ambient temperatures offers a particular challenge to the thermoregulatory system. It is likely that mechanisms such as sweat evaporation alone are not sufficient for maintaining body temperature within a safe limit (~36.5-38.5˚C) and below 40˚C, which may result in impaired physiological function and performance. Exogenous cooling may be of benefit prior to, during and after events that place increased thermal strain due to increased metabolic heat production and elevated environmental temperatures upon the thermoregulatory system. Conversely, in situations where it is not possible to maintain body temperature via either continued physical activity or elevated ambient temperatures, exogenous heating may be required in order to allow optimal physiological performance. Few studies have directly aligned cooling devices with data detailing effective target regions for cooling to allow a pre-cooling garment to be of minimal weight but maximal cooling efficiency. Conversely, no study has considered the effect of muscle temperature maintenance during rest periods on subsequent power-based activities. The aim of this thesis was to determine ways in which body temperature manipulation is capable of improving exercise performance in both power and endurance-based events. It was hypothesised that the manipulation of body temperature will result in subsequent changes in body temperature that would improve performance. Specifically, the use of pre-cooling would result in a reduction of body temperature and improve endurance exercise performance. Conversely, maintaining Tm following warm up completion would have a beneficial effect on sprint and power related performance. Study one set out to determine differences in regional body heat loss in 12 individual anatomical zones using a water perfused suit. Data obtained from this initial study allowed for the specific targeting of regions that were identified as having high rates of heat loss in subsequent studies that focused on pre-cooling and performance. The anatomical regions identified as having high potential affinity for heat exchange with the surrounding environment and cooling devices were the hands, forearms, upper and lower back and torso. Subsequent studies demonstrated that cooling of these areas was capable of lowering thermal sensation and improving thermal comfort prior to and during exercise in moderate environmental conditions (24˚C, 50% RH). In these moderate conditions, there was no statistically significant improvement in treadmill based self-paced 5000m running performance. However, in hot conditions (35˚C 50% RH), the use of a cooling vest and sleeves did yield a significant improvement in cycling time trial performance, which equated to 4.8%. This leads to the suggestion that there may be a threshold ambient temperature, above which pre-cooling becomes an important tool in maximizing performance potential. A parallel area of investigation, on the other side of the temperature spectrum, was the effect of muscle temperature manipulation on power-based exercise performance. The relationship between increased muscle temperature and power output is well established, however little is known about the effect of enforced rest or recovery between two bouts of exercise. Therefore, two studies were conducted to establish what affect a delay between warm up completion and exercise has on muscle temperature and subsequent sprint cycling performance. It was shown that with 30-minutes of rest between exercise bouts wearing tracksuit trousers, muscle temperature declined significantly (~1-1.5˚C). This decline was attenuated with the use of external passive electrical heating during the recovery compared to recovery completed in tracksuit trousers alone. The attenuated decline in muscle temperature following the use of the heated trousers resulted in an improvement in sprint cycling performance (~9%), with the use of insulated trousers having no effect on any variables measured, all relative to wearing tracksuit trousers in the rest period. In a follow-up study, the effect of implementing the heated trousers during the warm up and in addition to the rest period had on muscle temperature increase and sprint performance. A secondary area of investigation in this study was to determine the linearity of muscle temperature decline following warm up cessation. This study demonstrated that there was no additional benefit of combining passive heating with an active warm up on either muscle temperature elevations or subsequent sprint performance compared to the active warm up alone. It was shown that when the no heating was used at any stage, muscle temperature declined exponentially. However, when the heated trousers were used during recovery and/or during warm up, muscle temperature levelled off at a higher value towards the end of the recovery period. This study was also able to show significant improvements in absolute, relative and mean power output following the use of the heated trousers in the warm up and recovery, or the recovery alone. This thesis has identified ways in which body temperature may be manipulated in order to benefit both sprint and endurance exercise performance, using both pre-cooling and active heating. A novel concept for minimizing muscle temperature decline during periods of inactivity between different rounds of competition was shown to maximize sprint performance yielding significant improvements in peak and mean power outputs.



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A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.

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