Related Experiment Videos
Caffeine metabolism and epinephrine responses during exercise in users and nonusers
M H Van Soeren1, P Sathasivam, L L Spriet
1University of Guelph, Ontario, Canada.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|August 1, 1993
Summary
Caffeine users exhibit a blunted epinephrine response to exercise compared to nonusers, despite similar caffeine metabolism. Exercise itself elicits a greater epinephrine response in habitual caffeine users.
Area of Science:
- Exercise Physiology
- Nutritional Biochemistry
- Pharmacology
Background:
- Caffeine is a widely consumed ergogenic aid.
- Individual responses to caffeine vary.
- Understanding caffeine metabolism and physiological effects in users versus nonusers is crucial.
Purpose of the Study:
- To compare caffeine metabolism and catecholamine/metabolic responses between caffeine users and nonusers.
- To investigate the effects of acute caffeine ingestion during exercise.
Main Methods:
- Caffeine (5 mg/kg) or placebo administered during 1-hour steady-state exercise (50% VO2max).
- Caffeine users underwent controlled caffeine intake/abstinence protocols.
- Plasma catecholamines (epinephrine, norepinephrine), dimethylxanthines, free fatty acids, glycerol, and respiratory exchange ratio were measured.
Main Results:
- Caffeine increased plasma epinephrine in nonusers but not in users.
- Exercise elicited a twofold greater epinephrine response in users compared to nonusers (placebo trial).
- Plasma theophylline was higher in users, paraxanthine in nonusers; other metabolic markers were similar.
Conclusions:
- Habitual caffeine use attenuates the acute epinephrine response to caffeine ingestion during exercise.
- Exercise itself is a potent stimulus for epinephrine release, particularly in caffeine users.
- Differences in caffeine metabolism (e.g., paraxanthine levels) do not directly correlate with free fatty acid responses during exercise in this cohort.