Effects of Normobaric Hypoxia on Matched-severe Exercise and Power-duration Relationship

Abstract

We investigated the effects of hypoxia on matched-severe intensity exercise and on the parameters of the power-duration relationship. Fifteen trained subjects performed in both normoxia and normobaric hypoxia (FiO2=0.13, ~3000 m) a maximal incremental test, a 3 min all-out test (3AOT) and a transition from rest to an exercise performed to exhaustion (Tlim) at the same relative intensity (80%∆). Respiratory and pulmonary gas-exchange variables were continuously measured (K5, Cosmed, Italy). Tlim test’s V̇O2 kinetics was calculated using a two-component exponential model. V̇O2max (44.1±5.1 vs. 58.7±6.4 ml.kg-1.min-1, p<0.001) was decreased in hypoxia. In Tlim, time-to-exhaustion sustained was similar (454±130 vs. 484±169 s) despite that V̇O2 kinetics was slower (τ1: 31.1±5.8 vs. 21.6±4.7 s, p<0.001) and the amplitude of the V̇O2 slow component lower (12.4±5.4 vs. 20.2±5.7 ml.kg-1.min-1, p<0.05) in hypoxia. CP was reduced (225±35 vs. 270±49 W, p<0.001) but W’ was unchanged (11.3±2.9 vs. 11.4±2.7 kJ) in hypoxia. The changes in CP/V̇O2max were positively correlated with changes in W’ (r = 0.58, p<0.05). The lower oxygen availability had an impact on aerobic related physiological parameters, but exercise tolerance is similar between hypoxia and normoxia when the relative intensity is matched despite a slower V̇O2 kinetics in hypoxia.

Influence and Mechanisms of Action of Environmental Stimuli on Work Near and Above the Severe Domain Boundary (Critical Power)

“…Within the same study, resting and end-exercise blood oxygen saturation ( ), , and power output during ergometer trials designed to elicit fatigue in ~ 3 and ~ 15 min were all lower during exercise in acute hypoxia. Similar results are seen in trained cyclists; CP decreased (270 ± 49 to 225 ± 35 watts) in acute hypoxia ( 0.13) yet W ′ remained unchanged [ 16 ]. Correspondingly, in recreationally active females, CP is reduced (175 ± 25 to 132 ± 17 watts) in acute hypoxia ( 0.13) with W ′ remaining stable [ 17 ].…”

Dietary Nitrate Supplementation Is Not Helpful for Endurance Performance at Simulated Altitude Even When Combined With Intermittent Normobaric Hypoxic Training

“…In our study, at least for the HNO group, SmO 2min was significantly lower in T lim at post-compared to pre-intervention period. Although acute exposure to simulated altitude induces a slower O 2 kinetics ( Sousa et al, 2021 ), there are no studies that analyzed the chronic impact of hypoxic exposure on altitude’ O 2 kinetics performance.…”

“…Time sustained was determined through the T lim test and performed at 80%∆ (i.e., first ventilatory threshold—VT 1 , plus 80% of the difference between VT 1 and O 2 max). The test ended when the cadence could no longer be maintained within 10 rpm of the preferred cadence for >5 s. Critical power (CP) and the curvature constant (W′) were both assessed during the 3AOT test as previously described ( Sousa et al, 2021 ). In this test, during the last 5 s of the baseline period, subjects were asked to increase their cadence to approximately 110 rpm.…”

“…If a plateau of less than 2.1 ml·min −1 ·kg −1 could not be observed, the p O 2 max was calculated as previously described ( Kuipers et al, 1985 ). VT 1 and VT 2 were determined as previously suggested ( Sousa et al, 2021 ). The percentage of power, O 2 and HR relative to p O 2 max, O 2 max, and HRmax associated to both VT 1 and VT 2 (VT 1 -W, VT 1 -O 2 , VT 1 -HR, VT 2 -W, VT 2 -O 2 , and VT 2 -HR) were considered for analysis.…”

Effects of Hypoxia Responses during Moderate- and Severe-Intensity Exercise Performed to Exhaustion

“…Limited research has been done on severeintensity exercise at altitude or under hypoxic conditions. The tauprimary is slowed and Aprimary is reduced in hypoxia compared to normoxia (Millet et al 2021). The slowing of the VO2 kinetics in hypoxia is associated with a higher oxygen deficit compared to normoxia (McLellan et al 1990).…”