Metabolic and Ventilatory Effects of Caffeine During Light Intensity Exercise in Trained and Sedentary Low Habitual Caffeine Users

Abstract

This study examined selected physiological effects of caffeine during constant load, light intensity exercise in aerobically trained (TM) and sedentary (SM) low habitual caffeine users (<150 mg·day-1). Twelve healthy nonsmoking males (6 TM, 6 SM), following a 12-hr caffeine and food abstinence, participated in two separate 45-min trials consisting of constant load treadmill exercise at 30% of VO2max after caffeine (5 mg·kg-1) or placebo administered 60 min prior to experimental data acquisition. It was observed that pre-trial caffeine intake lowered respiratory exchange ratio (RER) and increased oxygen uptake (1·min- 1) and metabolic rate (kJ·min-1) during light intensity exercise (p<0.05). Minute ventilation (1 ·min- 1) and tidal volume (ml·min-1) was elevated in caffeine when compared to placebo trials (p<0.05). On the other hand, caffeine had no effect on frequency of breathing breath·min- 1) and carbon dioxide output via the lungs (1·min- 1). There was no statistically significant difference in physiological response to caffeine between the SM and TM subject groups for any of the variables studied. It is concluded that caffeine enhances fat oxidation, augments exercise metabolic rate, and alters ventilatory dynamics during light intensity exercise. The present findings indicate that these effects are similar in aerobically trained and sedentary low habitual caffeine consumers.