The Effects of Cool and Warm Temperature on Selected Physiological Variables.

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Environmental Physiology

The Effects of Cool and Warm Temperature on

Selected Physiological Variables

INTRODUCTION

The importance of ambient temperature on exercise performance is well documented. It is suggested that a cool environment may be beneficial in maintaining thermally tolerable conditions in spite of intense exercise (Werner, 1993). Additionally, several studies have acknowledged that exercise in the heat can impair performance (Febbraio et al. 1994; Nielsen et al. 1984).

Several studies have examined the physiological responses to heat and cold during exercise in order to account for these variations. Heat was reported to markedly increase VO2, heart rate and significantly elevate mean skin and core temperature (Galloway and Maughan, 1997). A higher ambient temperature is also seen to increase skin blood flow (Gonzalez-Alonso et al. 1999). This increased dependence of thermoregulation is seen to impair performance. Similarly, low ambient temperatures (0oC) have been reported to induce a decline in performance. Heart rate is lower and oxygen consumption is higher and muscle glycogen utilisation is lower. It has also been reported that cold can reduce maximum oxygen uptake (Bergh and Ekblom, 1979). Recent studies have suggested that the optimal temperature for exercise performance is around 11oC and that the relationship between exercise capacity and temperature follows an inverted U-relationship (Galloway and Maughan, 1997).

Therefore the aim of this investigation is to examine several physiological responses during a fixed intensity cycling bout under two contrasting environmental conditions. It is hypothesised that during the hot conditions there will be significant higher increases in heart rate, mean skin and core temperature, skin blood flow, lactate, VO2, RER and RPE compared to the cold. Furthermore we postulated that in the heat there will be significant larger decreases in weight loss and plasma volume due to increased sweating.  

     

METHODS

        

Subjects

        

The investigation was conducted on six healthy male subjects who had an average age of 22 + 2yrs, weight 78kg, and height 175cm. The subjects were informed of the demands of the sessions and the risks and discomforts associated with the testing before providing their consent in writing to participate.

General Design

        To identify the influence of temperature on physiological variables two studies were conducted. The first study was performed in cool conditions and the second in hot conditions. The tests were performed in an environmental chamber so that the temperature could be manipulated to suit. Throughout the test several techniques were adopted in order to measure changes in selected physiological variables. The intensity of the exercise was fixed for both tests (65% VO2 max).

Experimental Design

        The study required the subjects to perform two 30-minute exercise bouts on a cycle ergometer (model 814, E, Monark) in a hot environment (30oC) and cool conditions (15oC) at a controlled relative humidity of 50% for both. The temperature on each of these occasions was controlled in an environmental chamber in which the subjects performed. All subjects cycled at a fixed power of 150 watts and a speed of 60 RPM, which corresponds to an exercise intensity of approximately 65% VO2 max.

        On the day before the test the subjects adopted the same diet and refrained from any exercise. To avoid any circadian variation the two tests were performed at the same time of day. In addition to this the two experimental testing sessions were separated by a week to eliminate any training or fatiguing effects.

Measurements  

        Several baseline measurements were taken before the exercise bouts. This required the subjects to rest for at least 15 minutes, were after heart rate, blood lactate, mean skin and core temperature, and skin blood flow were taken. Continued measurement of heart rate, core temperature, skin blood flow, mean skin temperature, and RPE was conducted throughout the test with measurements being taken every 5 minutes.  Blood lactate, haemoglobin, haematocrit, VO2, and RER were also recorded after 15 mins and at the end of the bout. Nude body mass was recorded before and after to determine weight loss during exercise due to sweating.

Blood Sampling and Analysis: Blood samples were obtained using a softclix on the fingertips of each subject at rest and every 15 mins until the end of the exercise. For the resting sample the subject was required to sit for up to 15 minutes before blood was taken. Blood was taken so that lactate, haematocrit, and haemoglobin could be analysed. Lactate was measure in the Analox GM7 Pro Analyser and Haemoglobin was analysed using the Haemocue. The blood was also spun using a microcentrifuge so that haematocrit could be determined (Hawskey Analyser, England). Haematocrit and haemoglobin values were used to calculate plasma volume change (Dill and Costill, 1974).

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Skin Blood flow: Blood flow was determined throughout the test using a Perimed Laser Doppler flowmeter. The probe was taken on the dorsal side of the forearm and the values were recorded at rest and every 5 mins until the end of exercise.      

Core and Skin Temperature: Core temperature was measured using a First Temperature Genius placed in the ear. Readings were taken at rest and every five minutes during exercise. Skin temperature was determined by taking an average of three skin cites around the body. Skin thermistors were placed on the calf, forearm, and below ...

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