IMPROVED RUNNING PERFORMANCE IN HOT HUMID CONDITIONS FOLLOWING WHOLE-BODY PRECOOLING

On two separate occasions, eight subjects controlled treadmill speed t o run the greatest distance possible in 30 min in a hot, humid environ ment (ambient temperature 32 degrees C, relative humidity 60%). For th e experimental test (precooling), exercise was preceded by cold-water immersion. Precooling increased the distance run by 304 +/- 166 m (P < 0.05). Precooling decreased the pre-exercise rectal and mean skin tem perature by 0.7 degrees C and 5.9 degrees C, respectively (P < 0.05). Rectal and mean skin temperature were decreased up to 20 and 25 min du ring exercise, respectively (P < 0.05). Mean body temperature decrease d from 36.5 +/- 0.1 degrees C to 33.8 +/- 0.2 degrees C following prec ooling (P < 0.05) and remained lower throughout exercise (P < 0.01) an d at the end of exercise (by 0.8 degrees C; P < 0.05). The rate of hea t storage at the end of exercise increased from 113 +/- 45 to 249 +/- 55 W.m(-2) (P < 0.005). Precooling lowered the heart rate at rest (13% ), 5 (9%), and 10 min (10%) exercise (P < 0.05) and increased the end of exercise blood lactate from 4.9 +/- 0.5 to 7.4 +/- 0.9 mmol.L-1 (P < 0.01). The (V) over dot O-2 at 10 and 20 min of exercise and total b ody sweating were not different between tests. In conclusion, water im mersion precooling increased exercise endurance in hot, humid conditio ns with an enhanced rate of heat storage and decreased thermoregulator y strain.