Acid-base, metabolic, and ventilatory responses to repeated bouts of exercise

Acid-base, metabolic, and ventilatory responses to repeated bouts of exercise were examined. Ten male subjects performed two (T1, T2) 5-min work tests, on a cycle ergometer, separated by a 25-min rest. The results indicate the following. 1) T2 appears to have a larger aerobic energy component than T1, due to the fact that cumulative O2 uptake (Vo2) was significantly larger for T2 and that the immediate postexercise lactic acid (HLa) and delta HLa values were both significantly smaller for T2.2) CO2 production (Vco2) and the respiratory exchange ratio were both significantly lower for T2. This is probably due to greater fat metabolism and less nonmetabolic CO2 being produced from bicarbonate (HCO-3) buffering of HLa during T2.3) Even though Vco2 was significantly lower during T2, minute ventilation (VE) was not significantly different between T1 and T2. This suggests that the ventilatory response during exercise cannot be solely mediated via CO2 flux to the lungs. 4) HLa removal and (HCO-3) regeneration appear to be sequentially linked together as indicated by the almost identical mirror image and significant -0.93 correlation. In conclusion, it appears that a bout of high-intensity exercise (T1) can alter the acid-base and metabolic responses seen during subsequent performance (T2).