Effect of Hyperoxia on Critical Power and V˙O2 Kinetics during Upright Cycling

Abstract

Introduction/Purpose: Critical power (CP) is a fundamental parameter defining highintensity exercise tolerance, however its physiological determinants are incompletely understood. The present study determined the impact of hyperoxia on CP, the time constant of phase II pulmonary oxygen uptake kinetics (! O2), and muscle oxygenation (assessed by near-infrared spectroscopy) in 9 healthy men performing upright cycle ergometry. Methods: CP was determined in normoxia and hyperoxia (fraction of inspired O 2 = 0.5) via 4 severeintensity constant load exercise tests to exhaustion on a cycle ergometer, repeated once in each condition. During each test, ! O2 and the time constant of muscle deoxyhaemoglobin kinetics (τ [HHb]), alongside absolute concentrations of muscle oxyhaemoglobin ([HbO 2 ]), were determined. Results: CP was greater (hyperoxia: 216 ± 30 vs. normoxia: 197 ± 29W; P < 0.001) whereas W' was reduced (hyperoxia: 15.4 ± 5.2 kJ, normoxia: 17.5 ± 4.3 W; P = 0.037) in hyperoxia compared to normoxia. ! O2 (hyperoxia: 35 ± 12 vs normoxia: 33 ± 10 s; P = 0.33) and τ [HHb] (hyperoxia: 11 ± 5 vs. normoxia: 14 ± 5 s; P = 0.65) were unchanged between conditions, whereas [HbO 2 ] during exercise was greater in hyperoxia compared to normoxia (hyperoxia: 73 ± 20 vs. normoxia: 66 ± 15 µM; P = 0.001). Conclusion: This study provides novel insights into the physiological determinants of CP and by extension, exercise tolerance. Microvascular oxygenation and CP were improved during exercise in hyperoxia compared with normoxia. Importantly, the improved microvascular oxygenation afforded by hyperoxia did not alter ! O2 , suggesting that microvascular O 2 availability is an independent determinant of the upper limit for steady-state exercise, i.e. CP.

The Acute Effect of Hyperoxia on Onset of Blood Lactate Accumulation (OBLA) and Performance in Female Runners during the Maximal Treadmill Test

“…Furthermore, it has been mentioned that ATP was responsible for a part of the muscle vasodilation that followed muscle hyperemia during exercise [ 35 ]. On the other hand, we can relate our results to other reasons, probably attributable to the increase in microvascular and intracellular oxygenation during exercise when compared to normoxia [ 36 , 37 ]. In addition, Goulding et al [ 36 ] demonstrated an increase in the concentration of muscle oxyhemoglobin under the condition of hyperoxia, which is an important physiological determinant for increasing exercise extension and tolerance.…”

The ramp and all-out exercise test to determine critical power: validity and robustness to manipulations in body position

“…The data presented in the present study comprise retrospective analysis of data from five previous reports (Goulding et al 2017 , 2018a , b , 2019a , b ). A total of 26 participants completed the upright exercise experiments (Goulding et al 2017 , 2018a , 2019b ) and a total of 16 participants completed the supine exercise experiments (Goulding et al 2018b , 2019a ).…”

“…The data presented in the present study comprise retrospective analysis of data from five previous reports (Goulding et al 2017 , 2018a , b , 2019a , b ). A total of 26 participants completed the upright exercise experiments (Goulding et al 2017 , 2018a , 2019b ) and a total of 16 participants completed the supine exercise experiments (Goulding et al 2018b , 2019a ). However, several participants completed more than one of the original experiments, therefore in these instances only the data from the first experiment that the participant took part in was used for further analysis.…”

Limitations to exercise tolerance in type 1 diabetes: the role of pulmonary oxygen uptake kinetics and priming exercise

“…Priming exercise has the capacity to enhance both muscle O2 delivery and utilization at the onset of exercise (22,32,39). In Part 2, the effect of priming exercise on critical power could therefore have been via an independent effect of enhanced O2 availability, rather than a reduced ̇O2 per se (28). However, the reduction in τ[HHb+Mb (i.e.…”

“…Despite the importance of critical power in determining exercise tolerance, its physiological antecedents have previously remained poorly understood. However, data from our laboratory has shown in healthy individuals that critical power, and by extension exercise tolerance, is determined by the rate of increase in pulmonary oxygen uptake (̇O2, a proxy for muscle ̇O 2 kinetics, 26) at the onset of exercise (24)(25)(26)(27)(28), specifically the fundamental phase time constant (̇O2).…”