Oxygen delivery is not a limiting factor during post-exercise recovery in healthy young adults

Abstract

PurposeIt is still equivocal whether oxygen uptake recovery kinetics are limited by oxygen delivery and can be improved by supplementary oxygen. The present study aimed to investigate whether measurements of muscle and pulmonary oxygen uptake kinetics can be used to assess oxygen delivery limitations in healthy subjects.MethodsSixteen healthy young adults performed three sub-maximal exercise tests (6 min at 40% Wmax) under hypoxic (14%O2), normoxic (21%O2) and hyperoxic (35%O2) conditions on separate days in randomized order. Both Pulmonary VO2 and near infra red spectroscopy (NIRS) based Tissue Saturation Index (TSI) offset kinetics were calculated using mono-exponential curve fitting models.ResultsTime constant τ of VO2 offset kinetics under hypoxic (44.9 ± 7.3s) conditions were significantly larger than τ of the offset kinetics under normoxia (37.9 ± 8.2s, p = 0.02) and hyperoxia (37±6s, p = 0.04). TSI mean response time (MRT) of the offset kinetics under hypoxic conditions (25.5 ± 13s) was significantly slower than under normoxic (15 ± 7.7, p = 0.007) and hyperoxic (13 ± 7.3, p = 0.008) conditions.ConclusionThe present study shows that there was no improvement in the oxygen uptake and muscle oxygenation recovery kinetics in healthy subjects under hyperoxic conditions.Slower TSI and VO2 recovery kinetics under hypoxic conditions indicate that both NIRS and spiro-ergometry are appropriate non-invasive measurement tools to assess the physiological response of a healthy individual to hypoxic exercise.

Comparisons Between Normobaric Normoxic and Hypoxic Recovery on Post-exercise Hemodynamics After Sprint Interval Cycling in Hypoxia

“…In both conditions, the participants performed maximal cycling which resulted in successive intense ischemic episodes in the exercising muscle (i.e., StO 2 < 20%, Figure 4A ). Previous studies have evaluated muscle reoxygenation responses (oxygen delivery to tissues) after exercise ( Kemps et al, 2009 ; Mankowski et al, 2017 ; Zebrowska et al, 2021 ), and confirmed the validity and utility of NIRS device when assessing individuals’ recovery kinetics between different oxygen levels ( Mankowski et al, 2017 ). Arterial inflow to thigh muscles may have increased during recovery irrespective of different oxygen recovery conditions, and that normoxic recovery further enhanced these responses compared to hypoxic recovery, probably due to greater arterial O 2 supply (higher arterial O 2 content).…”