Metabolic and cardiovascular responses to exercise with caffeine

The effect of caffeine on circulation and metabolism was studied during a discontinuous maximal oxygen uptake (VO2 max) test on a bicycle ergometer. Eight male subjects were chosen for their minimal use of caffeine of which six normally did not ingest caffeinated beverages. Two caffeinated and two decaffeinated (control) trials were administered to each subject following double-blind and counterbalanced testing procedures. One hour before exercise, subjects ingested decaffeinated coffee with or without 350 mg of caffeine anhydrous added. Cardiac output (Q) was measured by a C02 rebreathing technique. Compared to control trials, caffeine increased the VO2 max by an average of 140ml min−1 (p <0-0·5)l. In addition, during caffeine trials, the average maximal heart rate (HR max) was elevated by 5 beats min−1 (p<0·01). There were no other statistically significant changes in metabolic (VO2 and R) and cardiovascular (Q, HR, SV and (a-v) 02 diff) variables during either submaximal or maximal exercise. Performance, as measured by total exercise time on the VO2 max test, was not significantly different (p>0·05). It was concluded that caffeine has a small physiological but a statistically significant effect on VQ2 max and HR max. During submaximal exercise, caffeine did not significantly effect the cardiovascular system.