- D D Brown: Department of Physical Education, Southern Illinois University, Carbondale.
The purpose of this study was to examine the effect of caffeine ingestion on alveolar ventilation and physiological dead space ventilation during exercise in high and low caffeine users. Eleven males (mean age 26.4 +/- 5.4 years), classified as either high caffeine users (greater than 350 mg/d, n = 6) or low caffeine users (less than 50 mg/d, n = 5) performed two treadmill exercise conditions at a constant work rate (50% VO2max) 45 min after ingestion of 3.3 mg of caffeine/kg body weight or placebo using a double-blind protocol. Open circuit spirometry was used to determine ventilatory and gas exchange variables every 10 min during the 50 min of walking exercise. Analysis of variance showed that caffeine produced significant differences in alveolar ventilation (VA) and the physiological dead space ventilation/tidal volume ratio (VD/VT) with VA increased from 1.36 to 1.54 L/breath and VD/VT decreased from 22.3 to 20.5% between the placebo and caffeine treatments, respectively. Additionally, caffeine ingestion produced a significant increase in tidal volume (VT) and a significant decrease in frequency of breathing (fb). We conclude that caffeine consumed prior to exercise enhances ventilatory dynamics during exercise without regard to prior habitual caffeine consumption.