Thermoregulatory responses to exercise in the heat: chronic caffeine intake has no effect.

摘要: INTRODUCTION: Authorities advise individuals to refrain from caffeine intake before or during exercise, especially when performed in the heat, due potential fluid-electrolyte imbalances that exaggerate physiological strain. Yet, military personnel are often deployed hot environments and must perform under sleep-deprived conditions where would be an ideal intervention strategy enhance physical cognitive performance. PURPOSE: To assess effects of controlled chronic acute ingestion on fluid-electrolyte, thermoregulatory responses exercise heat tolerance test (EHT). METHODS: Subjects were 59 active, college-aged males (mean +/- SE 21.6 0.4 yr, 177.9 0.8 cm, 75.4 1.0 kg, 11.1 0.7% body fat) who randomized stratified by age, bodyweight, composition into three groups. All subjects equilibrated at 3 mg x kg(-1) d(-1) for days 1-6. On 7-12, they consumed a treatment dose either 0 (G0), (G3), 6 (G6) d(-1). Fluid-electrolyte measures made day 12, 1 h after intake, EHT (90 min walking, 1.56 m s(-1), 5% grade; dry bulb temperature, 37.7 0.1 degree C; relative humidity, 56.3 -1.5%). RESULTS: There no between-group differences (p > 0.05) plasma, urinary, thermoregulatory, cardiovascular, perceptual variables across time (pre- vs. post-EHT), although some these increased significantly over < 0.05). was greater G3 (86 2.0 min) GO (75 3.3 min, p 0.05). DISCUSSION: Acute ingestion, chronically consuming (3 d(-1)) did not alter endurance compared with G0.