Elevated baseline work rate slows pulmonary oxygen uptake kinetics and decreases critical power during upright cycle exercise

Abstract Critical power is a fundamental parameter defining high‐intensity exercise tolerance, and is related to the phase II time constant of pulmonary oxygen uptake kinetics ( τ V ˙ O 2). Whether this relationship is causative is presently unclear. This study determined the impact of raised baseline work rate, which increases τ V ˙ O 2, on critical power during upright cycle exercise. Critical power was determined via four constant‐power exercise tests to exhaustion in two conditions: (1) with exercise initiated from an unloaded cycling baseline (U→S), and (2) with exercise initiated from a baseline work rate of 90% of the gas exchange threshold (M→S). During these exercise transitions, τ V ˙ O 2and the time constant of muscle deoxyhemoglobin kinetics ( τ [HHb + Mb] ) (the latter via near‐infrared spectroscopy) were determined. In M→S, critical power was lower (M→S = 203 ± 44 W vs. U→S = 213 ± 45 W, P  =   0.011) and τ V ˙ O 2was greater (M→S = 51 ± 14 sec vs. U→S = 34 ± 16 sec, P  =   0.002) when compared with U→S. Additionally, τ [HHb + Mb] was greater in M→S compared with U→S (M→S = 28 ± 7 sec vs. U→S = 14 ± 7 sec, P  =   0.007). The increase in τ V ˙ O 2and concomitant reduction in critical power in M→S compared with U→S suggests a causal relationship between these two parameters. However, that τ [HHb + Mb] was greater in M→S exculpates reduced oxygen availability as being a confounding factor. These data therefore provide the first experimental evidence that τ V ˙ O 2is an independent determinant of critical power. Keywords critical power, exercise tolerance, oxygen uptake kinetics, power‐duration relationship, muscle deoxyhemoglobin kinetics, work‐to‐work exercise.