title: Effects of caffeine, ephedrine and their combination on time to exhaustion during high-intensity exercise.
abstract: This study investigated the effects of acute ingestion of caffeine (C), ephedrine (E) and their combination (C+E) on time to exhaustion during high-intensity exercise. Using a repeated-measures, double-blind design, eight male subjects exercised on a cycle ergometer at a power output that led to exhaustion after about 12.6 min during a placebo (P) control trial. They did this 1.5 h after ingesting either C (5 mg x kg[-1]), E (1 mg x kg[-1]), C+E, or P. Trials were separated by 1 week. Venous blood was sampled before and during exercise. The mean (SD) times to exhaustion were 12.6 (3.1) (P), 14.4 (4.1) (C), 15.0 (5.7) (E) and 17.5 (5.8) (C+E) min. Only the C+E treatment significantly increased time to exhaustion compared to P. Oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE) and the respiratory exchange ratio (RER) were similar during exercise for all trials. Heart rate during exercise was significantly increased for the C+E and C trials compared to P. Subjective ratings of perceived exertion during exercise were significantly lower after C+E compared to P. All treatments significantly increased lactate levels. Free fatty acid (FFA) levels were significantly increased by C ingestion. Glycerol levels were increased by C+E and C ingestion. Glucose levels were also higher with the drug treatments compared to P. Increased monamine availability after C+E treatment was suggested by measurements of catecholamines and dopamine. In conclusion, the combination of C+E significantly prolonged exercise time to exhaustion compared to P, while neither C nor E treatments alone significantly changed time to exhaustion. The improved performance was attributed to increased central nervous system stimulation.
authors.affiliation: Defence and Civil Institute of Environmental Medicine, North York, Ontario, Canada.
authors.forename: D G
authors.initials: DG
authors.lastname: Bell
authors.forename: I
authors.initials: I
authors.lastname: Jacobs
authors.forename: J
authors.initials: J
authors.lastname: Zamecnik
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D002110:Caffeine / Q000008:administration & dosage* / Q000494:pharmacology*; D002245:Carbon Dioxide / Q000502:physiology; D004298:Dopamine / Q000097:blood; D004357:Drug Synergism; D004809:Ephedrine / Q000008:administration & dosage* / Q000494:pharmacology*; D004837:Epinephrine / Q000097:blood; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005990:Glycerol / Q000097:blood; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D018763:Muscle Fatigue / Q000187:drug effects* / Q000502:physiology; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology; D012119:Respiration / Q000187:drug effects; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D002245:Carbon Dioxide; D019344:Lactic Acid; D002110:Caffeine; D004809:Ephedrine; D005990:Glycerol; D004298:Dopamine; D009638:Norepinephrine; D004837:Epinephrine