THERMOREGULATORY EFFECTS OF CAFFEINE INGESTION DURING SUBMAXIMAL EXERCISE IN MEN

Background: The exclusive effect of caffeine ingestion on exercise the rmoregulation is unclear; data indicate that caffeine may have a posit ive effect, a negative effect, or no effect. Methods: Rectal (TRE) and mean skin ((T) over bar SK) temperatures, skin heat conductance (HSK) , and sweat rate ((M)over dot SW) were measured during 30 min of rest and subsequent 70 min of submaximal cycle-ergometer exercise (67% (V)o ver dot O(2)PEAK) in 11 aerobically conditioned men (mean +/- SD 29 +/ - 6 yr, 49 +/- 6 mL.min(-1).kg(-1) (V)over dot O(2)PEAK) under two con ditions: a caffeine (10 mg.kg(-1)) ingestion (CI) session and a noncaf feine ingestion (NCI) control session. Results: There were no signific ant differences in physiological or thermoregulatory parameters during exercise: (X) over bar (+/-SE) end exercise levels fur the NCI and CI sessions, respectively, were (V)over dot O-2 = 2.50 +/- 0.09 vs. 2.55 +/- 0.09 L.min(-1); heart rate = 145 +/- 7 vs. 145 +/- 5 bpm; HSK = 3 0 +/- 3 vs. 28 +/- 3 kcal.m(-2).h(-1).degrees C-1; (M)over dot SW = 39 3 +/- 35 vs. 378 +/- 36 g.m(-2).h(-1); and TRE = 38.3 +/- 0.2 vs. 38.4 +/- 0.1 degrees C. Control (T) over bar SK was lower than that fur CI by 0.4 to 0.5 degrees C at rest and during exercise. Conclusion: Inge stion of a high level (10 mg.kg(-1)) of caffeine has no effect on skin heat conductance, sweating, or the rate of increase and final level o f rectal temperature during moderate, submaximal leg exercise.