Coupling of (V)over dot(E) and (V)over dotCO(2) kinetics: insights from multiple exercise transitions below the estimated lactate threshold

During a step-change in exercise power output (PO), ventilation ((V)over dot(E)) increases with a similar . time course to the rate of carbon dioxide delivery to the lungs ((V)over dotCO(2)). To test the strength of this coupling, we compared (V)over dot(E) and (V)over dotCO(2) kinetics from ten independent exercise transitions performed within the moderate-intensity domain. Thirteen males completed 3-5 repetitions of Delta 40 W step transitions initiated from 20, 40, 60, 80, 100, and 120 W on a cycle ergometer. Preceding the Delta 40 W step transitions from 60, 80, 100, and 120 W was a 6 min bout of 20 W cycling from which the transitions of variable Delta PO were examined. Gas exchange ((V)over dotCO(2) and oxygen uptake, (V)over dotO(2) ) and (V)over dot(E) were measured by mass spectrometry and volume turbine. The kinetics of the responses were characterized by the time constant (tau) and amplitude (Delta(V)over dot(E)/Delta(V)over dotCO(2)). Overall, (V)over dotCO(2) kinetics were consistently slower than (V)over dotO(2) kinetics (by similar to 45%) and tau(V)over dotCO(2) rose progressively with increasing baseline PO and with heightened Delta PO from a common baseline. Compared to tau(V)over dotCO(2) , tau(V)over dot(E) was on average slightly greater (by similar to 4 s). Repeated-measures analysis of variance revealed that there was no interaction between tau(V)over dotCO(2) and tau(V)over dot(E) in either the variable baseline (p = 0.49) and constant baseline (p = 0.56) conditions indicating that each changed in unison. Additionally, for Delta(V)over dot(E)/Delta(V)over dotCO(2), there was no effect of either variable baseline PO (p = 0.05) or increasing Delta PO (p = 0.16). These data provide further evidence that, within the moderate-intensity domain, both the temporal- and amplitude-based characteristics of (V)over dot(E) kinetics are inextricably linked to those of (V)over dotCO(2).