Context: Cooling the body before exercise (precooling) has been studied as an ergogenic aid for many thermal conditions; however, airflow accompanying exercise is seldom reported.
Objective: To determine whether the physiologic and ergogenic benefits of precooling before endurance exercise may be negated with semirealistic airflow in hot conditions.
Design: Crossover study.
Setting: Climate-controlled chamber in a research laboratory.
Patients or other participants: Ten fit, healthy cyclists.
Intervention(s): After a familiarization trial, participants completed 4 randomized, counterbalanced sessions consisting of no precooling versus precooling and no fan airflow versus airflow (~4.8 m/s) during exercise. Precooling was via chest-deep immersion (~24 °C) for 1 hour or until core temperature dropped 0.5 °C. Participants then cycled at 95% ventilatory threshold in a hot environment (temperature = 30 °C, relative humidity = 50%) until volitional exhaustion, core temperature reached >39.5 °C, or heart rate reached >95% of maximum.
Main outcome measure(s): Thermal strain was assessed via core temperature (esophageal and rectal thermistors) and mean skin temperature (thermistors at 10 sites) and cardiovascular strain via heart rate and ratings of perceived exertion.
Results: Endurance time (28 ± 12 minutes without precooling or airflow) increased by 30 ± 23 minutes with airflow (~109%; 95% confidence interval = 12, 45 minutes; P < .001) and by 16 ± 15 minutes with precooling (~61%; 95% confidence interval = 4, 25 minutes; P = .013), but it was not further extended when the strategies were combined (29 ± 21 minutes longer than control). During cycling without precooling or airflow, mean core and skin temperatures were higher than in all other trials. Precooling reduced heart rate by 7-11 beats/min during the first 5 minutes of exercise, but this attenuation ended by 15 minutes.
Conclusions: Most laboratory-based precooling studies have (inadvertently) overestimated the extent of the physiologic and ergogenic benefits for typical athlete-endurance situations. Precooling increases work capacity effectively when airflow is restricted but may have little or no benefit when airflow is present.
Keywords: cardiovascular strain; convection; cooling; endurance; exercise; thermoregulation.