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 (V̇O₂max), ventilation, heart rate, respiratory exchange ratio (R), work rate, and blood lactate were not affected by caffeine. Submaximal exercise V̇O₂, 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 < 0.05). The lower exercise heart rate at the same V̇O₂ resulted in a significantly greater O₂ pulse during all submaximal exercise intensities for the caffeine trial (P < 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', Δl 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 · min^-1) was significantly (P < 0.05) lower than during the control trial (2.71 ± 0.17 l·min^-1). Therefore, rejection of our hypothesis was independent of the definition of the LT. However, conclusions regarding the opposite hypothesis (i.e., that caffeine would lower the LT) were dependent upon the definition of the LT.