Abstract
This study investigated the effect of reduced inspired fraction of O2 (FiO2) in the correspondence between the respiratory compensation point (RCP) and the breakpoint in the near‐infrared spectroscopy‐derived deoxygenated hemoglobin signal ([HHb]bp) during a ramp‐incremental (RI) test to exhaustion. Eleven young males performed, on two separated occasions, a RI test either in normoxia (NORM, FiO2 = 20.9%) or hypoxia (HYPO, FiO2 = 16%). Oxygen uptake ( V˙O2), and [HHb] signal from the vastus lateralis muscle were continuously measured. Peak V˙O2 (2.98 ± 0.36 vs. 3.39 ± 0.26 L min−1) and PO (282 ± 29 vs. 310 ± 19 W) were lower in HYPO compared to NORM condition, respectively. The V˙O2 and PO associated with RCP and [HHb]bp were lower in HYPO (2.35 ± 0.24 and 2.34 ± 0.26 L min−1; 198 ± 37 and 197 ± 30 W, respectively) when compared to NORM (2.75 ± 0.26 and 2.75 ± 0.28 L min−1; 244 ± 29 and 241 ± 28 W, respectively) (p < .05). Within the same condition, the V˙O2 and PO associated with RCP and [HHb]bp were not different (p > .05). Bland–Altman plots mean average errors between RCP and [HHb]bp were not different from zero in HYPO (0.01 L min−1 and 1.1 W) and NORM (0.00 L min−1 and 3.6 W) conditions. The intra‐individual changes between thresholds associated with V˙O2 and PO in HYPO from NORM were strongly correlated (r = .626 and 0.752, p < .05). Therefore, breathing a lower FiO2 during a RI test resulted in proportional reduction in the RCP and the [HHb]bp in terms of V˙O2 and PO, which further supports the notion that these physiological responses may arise from similar metabolic changes reflecting a common phenomenon.
Highlights
During a ramp-incremental (RI) test to exhaustion, the rate of O2 uptake (V O2) increases rather linearly from the exercise onset until maximal V O2 (V O2max) or task failure ensue
The absolute values for V O2 associated with the respiratory compensation point (RCP) and the [HHb]bp were lower in HYPO compared to NORM condition
This study investigated whether the strong relationship between the RCP and the [HHb]bp that is typically observed in normoxia during a RI test (Fontana et al, 2015; Iannetta, Qahtani, Maturana, & Murias, 2017; Iannetta, Qahtani, Millet, et al, 2017; Inglis et al, 2019; Keir et al, 2015; Murias, Keir, Spencer, & Paterson, 2013) was affected by breathing hypoxic air (FiO2 16%)
Summary
During a ramp-incremental (RI) test to exhaustion, the rate of O2 uptake (V O2) increases rather linearly from the exercise onset until maximal V O2 (V O2max) or task failure ensue. The RCP is identified as the onset of a more rapid increase in minute ventilation that is disproportional from the rate of carbon dioxide production (VCO2), which causes the arterial tension of CO2 to fall (Whipp et al, 1989). This hyperventilatory response offers partial compensation to the blood accumulation of hydrogen ions ([H+]) arising from the accelerated glycolytic rate within the active musculature (Whipp et al, 1989). Others have proposed that the occurrence of the plateau in the [HHb] signal might be due to other physiological factors, such as the achievement of the upper limit for O2 extraction in the superficial portions of muscle (Okushima et al, 2015), and/or limitations to perfusive or diffusive provision of O2 during high-intensity exercise (Okushima et al, 2020)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
