McKenzie, J. M., Brammer, C. L., & Stager, J. M. (2014). Thermoregulatory challenges during warm-water exercise. Medicine & Science in Sports & Exercise, 46(5), Supplement abstract number 712.

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“Exercising in water creates a unique challenge to thermoregulation - high specific heat effectively clamps the skin temperature to the water temperature, eliminating the temperature gradient and limiting convection and conduction; and eliminates radiation and evaporation as avenues for heat exchange.”

This study examined the effects of exercise in water of critical temperatures as determined by various swimming authorities in endurance-trained males (N = 8). Ss performed one maximal cycling-exercise test, and three sessions of immersed cycling at water temperatures of 25.5°, 29.5°, and 31°C. Each experimental session lasted up to 60 minutes, at a heart rate of 131.3 ± 11.5 bpm. Ss were instructed to abstain from exercise 24 hours before each test. Maximal oxygen uptake, ventilation, and heart rate were collected during the maximal exercise test. During the three experimental sessions, heart rate, oxygen uptake, and ventilation were collected, as well as core body temperature, and water temperature. Physiological Strain Index was calculated using core temperature and heart rate for each test.

Significant differences were found in physiological strain index, heart rate, and weight loss during the exercise trials. Post-hoc analysis indicated that the 31°C trial was different from the 25.5° and 29.5°C trials for heart rate, physiological strain, and weight loss. Core temperature was not significantly different at the end of the exercise trials. There were no differences in physiological conditions at the beginning of exercise.

Implication. The differences in physiological strain index for each of the exercise trials appears to be due to differences in heart rate since core temperature showed no significant differences. The strain-index values suggest a moderate level of physiological strain.

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