EFFECTS OF ACUTE CAFFEINE WITHDRAWAL ON HABITUATED MALE RUNNERS

Effects of acute caffeine withdrawal on habituated male runners. J. Ap pl. Physiol. 76(3): 1043-1048, 1994. - This study investigated the eff ects of caffeine withdrawal on six trained caffeine-habituated male ru nners: age 29.8 +/- 5.8 (SD) yr, height 180.4 +/- 5.4 cm, weight 77.3 +/- 6.7 kg, maximal O-2 uptake 63.0 +/- 5.4 ml.kg(-1) min(-1), and dai ly caffeine intake 674 +/- 128 mg. The subjects received a loading dos e (5 mg/kg body wt) of caffeine 48 h before each testing session. They were then given (using a repeated-measures double-blind design) addit ional doses of caffeine (5 mg/kg body wt) or a placebo 36, 24, 12, and 2 h before testing. They ran at a velocity corresponding to their lac tate threshold for 60 min in a caffeine withdrawal or caffeinated cond ition. Caffeine withdrawal resulted in no significant differences in a bsolute O-2 uptake, O-2 uptake relative to maximal O-2 uptake, respira tory exchange ratios, or free fatty acid concentrations. Glycerol conc entrations were significantly attenuated in the withdrawal condition. No significant differences were revealed in calculated substrate utili zation. It was concluded that caffeine withdrawal significantly affect s lipolysis but not substrate utilization during prolonged running.