The metabolic response to caffeine in men with high and low aerobic power

Abstract

Increasing energy expenditure is one established method for treating obesity. Exercise training and caffeine consumption are two methods used to increase metabolic rate, however, their combined influence is not well understood. Poehlman et al. (Med. Sci. Sports Exerc., 17:689-94, 1985) reported a significantly greater increase in resting metabolic rate (RMR) following caffeine ingestion in untrained subjects (13.7%) as compared to their trained counterparts (7.2%). Opposingly, LaBlanc et al. (J. Appl. Physiol., 59:832-7, 1985) reported that trained subjects had a greater RMR increase (18.3%) following caffeine ingestion than did untrained subjects (13.7%). Differences in methodology and lack of some controls may account for the discrepancy in these two reports. The purpose of the present study was to compare the metabolic response to caffeine intake in men with high and low aerobic capacities with controls for caffeine habituation, dose of caffeine, and prior exercise. Sixteen men were classified as either having high (H, VO2max >55 ml/kg/min) or low (L, V 0 2max < 48 ml/kg/min) aerobic power using a maximal graded exercise test and as caffeine users or nonusers via a questionnaire. On two separate days after a 10 hour overnight fast RMR was measured using an indirect calorimetry open circuit system. Subjects orally consumed either a beverage containing caffeine (6 mg/kg lean body mass) or a placebo after which volume of oxygen consumed (V02), respiratory exchange ratio (RER), inspired ventilations (VE), heart rate (HR), and systolic blood pressure (SBP) were monitored for 180 minutes. Data were analyzed via a 3-way ANOVA with repeated measures. During the placebo trial no significant differences were observed in V02, VE, HR, or SBP between the H and L groups. Following caffeine consumption no significant interaction between fitness level and caffeine habits were observed for any of the dependent variables. Although VO2, VE, HR, and SBP all increased significantly following caffeine consumption, there were no significant main-effect differences between the H and L groups or between caffeine users and nonusers. However, there was a trend that the H group experienced a greater increase in V02 than the L group over the 180 minutes (+.039 vs. +.027 L/min, respectively). Also, the change in RER of the H group (-.03) was significantly lower than the L group (+.03) over the 180 minutes. Although there was some indication that H subjects had a heightened response to caffeine, the sensitivity of the measures could not conclusively demonstrate this. Further investigation of the influence of aerobic power on the metabolic response to caffeine with more sensitive indicators would be warranted.