Influence of caffeine on blood lactate response during incremental exercise.

To test the hypothesis that caffeine ingestion prior to exercise would delay the onset of blood lactate accumulation, eight male subjects were studied during incremental exercise to maximal work rates on a cycle ergometer under two conditions: 1 h after ingestion of 200 ml of either decaffeinated, calorie-free cola (control trial) or the same cola drink with 5 mg caffeine/kg body weight added (caffeine trial). Maximal exercise values for oxygen consumption (VO2 max), ventilation, heart rate, respiratory exchange ratio (R), work rate, and blood lactate were not affected by caffeine. Submaximal exercise VO2, ventilation, and R also were unaffected by caffeine. During the caffeine trial, submaximal exercise blood lactate was significantly higher and heart rate significantly lower than during the control trial (P less than 0.05). The lower exercise heart rate at the same VO2 resulted in a significantly greater O2 pulse during all submaximal exercise intensities for the caffeine trial (P less than 0.05). Data on R indicated that caffeine had no effect on substrate utilization during exercise. Data on exercise blood lactate response suggested that caffeine does not delay and may accelerate the onset of blood lactate accumulation during incremental exercise. When defined as either a "breakpoint," delta l mM (above resting lactate), or fixed level of 4 mM, the lactate threshold (LT) did not differ between caffeine and control trials. However, in using a 2 mM lactate level as a criterion, the LT during the caffeine trial (2.13 +/- 0.22 l X min-1) was significantly (P less than 0.05) lower than during the control trial (2.71 +/- 0.17 l X min-1).(ABSTRACT TRUNCATED AT 250 WORDS)