Effects Of Caffeine Intake Before Exercise On Substrate Metabolism During Exercise At Different Intensities

PurposeThe aim of this study was to explore whether the enhanced lipolysis of caffeine could further increase the fat oxidation and utilization during exercise by observing the effect of caffeine intake before exercise at different intensity on substrate metabolism and to analyze the metabolic characteristics of substrates-fat(FAT)and carbohydrates(CHO)during different intensity exercise.The study could provide a sports nutrition reference to the people who wish to lose fat and weight.MethodSixteen male college students were selected as subjects.The maximum oxygen uptake(VO2max)of the subjects was measured by incremental exercise test on the cycle ergometer,and the exercise intensities corresponding to 40% VO2 max and 70% VO2 max of each subject were calculated.A random,double-blind,crossover experiment was designed to perform a 1 h constant load exercise test.Caffeine tablets(5mg/kg BW)or dietary fiber tablets(placebo)were taken 1 h before each exercise,followed by 1 h of continuous exercise at intensity of 40% VO2 max or 70% VO2 max on the cycle ergometer.Subjects were required to participate in 4 constant load exercise trials: caffeine+40% VO2 max exercise,placebo+40% VO2 max exercise,caffeine+70% VO2 max exercise,placebo+70% VO2 max exercise.Before ingesting the substance,in a resting state after ingesting the substance,and in the subsequent 1 h constant load exercise,the respiratory gas was collected to analyze the substrate metabolism(FAT and CHO oxidation rate,change value of FAT and CHO oxidation rate,energy consumption),and blood biochemical indicators(plasma glycerol,blood lactate,blood sugar)and physiological indicators(heart rate,blood pressure)were determined.ResultIn the resting state,compared with the placebo intake,the plasma glycerin concentration,energy expenditure,systolic blood pressure and diastolic blood pressure were significantly increased after caffeine intake.The other indicators(heart rate,FAT and CHO oxidation rate,change value of FAT and CHO oxidation rate,blood lactic acid,blood sugar)were not significantly different between caffeine intake and placebo intake.During exercise at intensity of 40% VO2 max,compared with placebo intake,change value of FAT oxidation rate,blood lactate concentration,blood glucose concentration,systolic blood pressure were significantly increased,while change value of CHO oxidation rate was significantly decreased after caffeine intake.The other indicators(plasma glycerol concentration,heart rate,diastolic blood pressure,FAT and CHO oxidation rate)were not significantly different between caffeine intake and placebo intake.During exercise at intensity of 70% VO2 max,compared with placebo intake,blood glucose and blood lactate concentration were significantly increased after caffeine intake,and the other indicators(heart rate,blood pressure,plasma glycerol,FAT and CHO oxidation rate,change value of FAT and CHO oxidation rate)were not significantly different between caffeine intake and placebo intake.ConclusionCaffeine intake(5mg/kg BW)1 h before exercise could affect substrate metabolism,increase FAT oxidation and decrease CHO oxidation during subsequent 1 h exercise at 40% VO2 max intensity;but could not affect substrate metabolism during subsequent 1 h exercise at 70% VO2 max intensity.