INTERACTIONS OF PHYSICAL-TRAINING AND HEAT ACCLIMATION - THE THERMOPHYSIOLOGY OF EXERCISING IN A HOT CLIMATE

Physical training and heat acclimation are both commonly adopted tacti cs to improve performance and/or tolerance times when individuals must compete or work in the heat. Potential benefits include: (i) improved aerobic fitness and thus a greater cardiovascular reserve (probably s een mainly after training); (ii) a lower resting body temperature that allows greater heat storage (probably seen mainly after acclimation); (iii) a decreased energy cost of a given intensity of exercise (seen after acclimation and also as the learning component of training); (iv ) an enhanced sweating response at a given percentage of maximal effor t (probably developed by both treatments); (v) a slower increase in bo dy temperature owing to (iii) and/or (iv) [seen after both treatments] ; (vi) a reduced cardiovascular stress because of changes in the auton omic nervous system (probably realised mainly by training), expansion of blood volume (seen after both treatments) and/or a decreased periph eral pooling of blood (probably found after both treatments); and (vii ) improved subjective tolerance reflecting a decrease in the relative intensity of a given activity (probably seen mainly after training), a reduction in the physiological strain (found after both treatments) a nd/or habituation to heat-exercise stress (probably developed by both treatments). Factors affecting improvements in physiological and psych ological responses to a given set of conditions include: (i) the indiv idual's initial fitness and acclimatisation to heat; (ii) age, gender, hydration, sleep deprivation, circadian rhythms and in women the mens trual cycle; (iii) use of ergogenic aids such as fluid ingestion, carb ohydrate and/or electrolyte replacement and blood doping; (iv) event o r test conditions such as the mode of exercise, the severity of enviro nmental heat stress and the type of clothing worn; and (v) treatment c onditions such as the intensity, duration and frequency of exercise an d/or heat exposure, the length of any rest intervals and cumulative de pletion of body water and minerals.