EFFECTS OF CAFFEINE, EPHEDRINE AND THEIR COMBINATION ON TIME TO EXHAUSTION DURING HIGH-INTENSITY EXERCISE

This study investigated the effects of acute ingestion of caffeine (C) , ephedrine (E) and their combination (C + E) on time to exhaustion du ring 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 . kg(-1)), E (1 mg . kg(-1)). C+E, or P. Trials were separated by 1 week . Venous blood was sampled before and during exercise. The mean (SD) t imes 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 in creased time to exhaustion compared to P. Oxygen consumption ((V) over dot O-2), carbon dioxide production ((V) over dot CO2), minute ventil ation ((V) over dot (E)) and the respiratory exchange ratio (RER) were similar during exercise for all trials. Heart rate during: exercise w as significantly increased for the C + E and C trials compared to P. S ubjective ratings of perceived exertion during exercise were significa ntly lower after C + E compared to P. All treatments significantly inc reased 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 concl usion, the combination of C + E significantly prolonged exercise time to exhaustion compared to P, while neither C nor E treatments alone si gnificantly changed time to exhaustion. The improved performance was a ttributed to increased central nervous system stimulation.