scholarly journals The effect of the fraction of inspired oxygen on the NIRS-derived deoxygenated hemoglobin “breakpoint” during ramp-incremental test

2020 ◽  
Vol 318 (2) ◽  
pp. R399-R409 ◽  
Author(s):  
Rafael de Almeida Azevedo ◽  
Jorge E. Béjar Saona ◽  
Erin Calaine Inglis ◽  
Danilo Iannetta ◽  
Juan M. Murias
Keyword(s):  
Near Infrared ◽  
Vastus Lateralis ◽  
Linear Increase ◽  
Vastus Lateralis Muscle ◽  
Physiological Mechanisms ◽  
Incremental Test ◽  
Physically Active ◽  
Fraction Of Inspired Oxygen ◽  
Inspired Oxygen ◽  
Deoxygenated Hemoglobin

During ramp-incremental (RI) exercise to exhaustion, the near-infrared spectroscopy-derived deoxygenated hemoglobin ([HHb]) signal in the vastus lateralis muscle shows a linear increase up to a point at which a plateau-like response is manifested ([HHb]bp). This study investigated if 1) the [HHb]bp is affected by different fractions of inspired O2 ([Formula: see text]) [hypoxia (16%; HYPO); normoxia (21%; NORM); hyperoxia (30%; HYPER)]; and 2) an abrupt change to hyperoxic-inspired gas just before the occurrence of the [HHb]bp (HYPERSWITCH) would affect the [HHb] plateau-like response. Ten physically active male participants reported to the laboratory on four separate occasions to perform an RI test to exhaustion in NORM, HYPO, and HYPER and an RI test to exhaustion with an abrupt increase in [Formula: see text] (30%; HYPERSWITCH) 15 W before the power output (PO) associated with [HHb]bp in normoxia. PO, [HHb], tissue O2 ([Formula: see text]), and pulse O2 saturation ([Formula: see text]) were recorded continuously. Peak PO was significantly lower in HYPO (290 ± 21 W) and higher in HYPER (321 ± 22 W) and HYPERSWITCH (320 ± 19 W) compared with NORM (311 ± 18 W). The PO associated with [HHb]bp was not different between NORM and HYPER (246 ± 23 vs. 247 ± 24 W), but it was lower in HYPO (198 ± 31 W) than NORM and HYPER. The PO associated with the [HHb]bp in HYPERSWITCH (240 ± 23) was not different compared with NORM. HYPER and HYPERSWITCH resulted in greater [Formula: see text] and [Formula: see text] compared with NORM. These results suggest that the [HHb]bp response is not dependent of O2 driving pressure and that other physiological mechanisms might determine its occurrence.

scholarly journals Blood flow occlusion-related O2 extraction “reserve” is present in different muscles of the quadriceps but greater in deeper regions after ramp-incremental test

2018 ◽  
Vol 125 (2) ◽  
pp. 313-319 ◽  
Author(s):  
Danilo Iannetta ◽  
Dai Okushima ◽  
Erin Calaine Inglis ◽  
Narihiko Kondo ◽  
Juan M Murias ◽  
...  
Keyword(s):  
Blood Flow ◽  
Near Infrared ◽  
Vastus Lateralis ◽  
Rectus Femoris ◽  
Incremental Exercise ◽  
Vastus Lateralis Muscle ◽  
Incremental Test ◽  
Time Resolved ◽  
Blood Flow Occlusion ◽  
Flow Occlusion

It was recently demonstrated that an O2 extraction reserve, as assessed by the near-infrared spectroscopy (NIRS)-derived deoxygenation signal ([HHb]), exists in the superficial region of vastus lateralis (VL) muscle during an occlusion performed at the end of a ramp-incremental test. However, it is unknown whether this reserve is present and/or different in magnitude in other portions and depths of the quadriceps muscles. We tested the hypothesis that an O2 extraction reserve would exist in other regions of this muscle but is greater in deep compared with more superficial portions. Superficial (VL-s) and deep VL (VL-d) as well as superficial rectus femoris (RF-s) were monitored by a combination of low- and high-power time-resolved (TRS) NIRS. During the occlusion immediately post-ramp-incremental test there was a significant overshoot in the [HHb] signal ( P < 0.05). However, the magnitude of this increase was greater in VL-d (93.2 ± 42.9%) compared with VL-s (55.0 ± 19.6%) and RF-s (47.8 ± 14.0%) ( P < 0.05). The present study demonstrated that an O2 extraction reserve exists in different pools of active muscle fibers of the quadriceps at the end of a ramp exercise to exhaustion. The greater magnitude in the reserve observed in the deeper portion of VL, however, suggests that this portion of muscle may present a greater surplus of oxygenated blood, which is likely due to a greater population of slow-twitch fibers. These findings add to the notion that the plateau in the [HHb] signal toward the end of a ramp-incremental exercise does not indicate the upper limit of O2 extraction. NEW & NOTEWORTHY Different portions of the quadriceps muscles exhibited an untapped O2 extraction reserve during a blood flow occlusion performed at the end of a ramp-incremental exercise. In the deeper portion of the vastus lateralis muscle, this reserve was greater compared with superficial vastus lateralis and rectus femoris. These data suggest that the O2 extraction reserve may be dependent on the vascular and/or oxidative capacities of the muscles.

Association Between Deoxygenated Hemoglobin Breaking Point, Anaerobic Threshold, and Rowing Performance

2019 ◽  
Vol 14 (8) ◽  
pp. 1103-1109
Author(s):  
Tiago Turnes ◽  
Rafael Penteado dos Santos ◽  
Rafael Alves de Aguiar ◽  
Thiago Loch ◽  
Leonardo Trevisol Possamai ◽  
...  
Keyword(s):  
Heart Rate ◽  
Anaerobic Threshold ◽  
Power Output ◽  
Vastus Lateralis ◽  
Lactate Concentration ◽  
Blood Lactate Concentration ◽  
Breaking Point ◽  
Vastus Lateralis Muscle ◽  
Incremental Test ◽  
Deoxygenated Hemoglobin

Purpose: To compare the intensity and physiological responses of deoxygenated hemoglobin breaking point ([HHb]BP) and anaerobic threshold (AnT) during an incremental test and to verify their association with 2000-m rowing-ergometer performance in well-trained rowers. Methods: A total of 13 male rowers (mean [SD] age = 24 [11] y and  = 63.7 [6.1] mL·kg−1·min−1) performed a step incremental test. Gas exchange, vastus lateralis [HHb], and blood lactate concentration were measured. Power output, , and heart rate of [HHb]BP and AnT were determined and compared with each other. A 2000-m test was performed in another visit. Results: No differences were found between [HHb]BP and AnT in the power output (236 [31] vs 234 [31] W; Δ = 0.7%), 95% confidence interval [CI] 6.7%), (4.2 [0.5] vs 4.3 [0.4] L·min−1; Δ = −0.8%, 95% CI 4.0%), or heart rate (180 [16] vs 182 [12] beats·min−1; Δ = −1.6%, 95% CI 2.1%); however, there was high typical error of estimate (TEE) and wide 95% limits of agreement (LoA) for power output (TEE 10.7%, LoA 54.1–50.6 W), (TEE 5.9%, LoA −0.57 to 0.63 L·min−1), and heart rate (TEE 2.4%, LoA −9.6 to 14.7 beats·min−1). Significant correlations were observed between [HHb]BP (r = .70) and AnT (r = .89) with 2000-m mean power. Conclusions: These results demonstrate a breaking point in [HHb] of the vastus lateralis muscle during the incremental test that is capable of distinguishing rowers with different performance levels. However, the high random error would compromise the use of [HHb]BP for training and testing in rowing.

Effects of acute hypoxia on the oxygen uptake kinetics of older adults during cycling exercise

2012 ◽  
Vol 37 (4) ◽  
pp. 744-752 ◽  
Author(s):  
Livio Zerbini ◽  
Alfredo Brighenti ◽  
Barbara Pellegrini ◽  
Lorenzo Bortolan ◽  
Tommaso Antonetti ◽  
...  
Keyword(s):  
Older Adults ◽  
Oxygen Uptake ◽  
Near Infrared ◽  
Vastus Lateralis ◽  
Oxygen Uptake Kinetics ◽  
Uptake Kinetics ◽  
Moderate Intensity ◽  
Vastus Lateralis Muscle ◽  
Incremental Test ◽  
Square Wave

Pulmonary oxygen uptake, heart rate (HR), and deoxyhemoglobin (HHb) kinetics were studied in a group of older adults exercising in hypoxic conditions. Fourteen healthy older adults (aged 66 ± 6 years) performed 4 exercise sessions that consisted of (i) an incremental test to exhaustion on a cycloergometer while breathing normoxic room air (fractional inspired oxygen (FiO2) = 20.9% O2); (ii) an incremental test to exhaustion on a cycloergometer while breathing hypoxic room air (FiO2 = 15% O2); (iii) 3 repeated square wave cycling exercises at moderate intensity while breathing normoxic room air; and (iv) 3 repeated square wave cycling exercises at moderate intensity while breathing hypoxic room air. During all exercise sessions, pulmonary gas exchange was measured breath-by-breath; HHb was determined on the vastus lateralis muscle by near-infrared spectroscopy; and HR was collected beat-by-beat. The pulomary oxygen uptake kinetics became slower in hypoxia (31 ± 9 s) than in normoxia (27 ± 7 s) because of an increased mismatching between O2 delivery to O2 utilization at the level of the muscle. The HR and HHb kinetics did not change between hypoxia and normoxia,

Time-course of V̇O2 kinetics responses during moderate-intensity exercise subsequent to HIIT vs moderate-intensity continuous training in type 2 diabetes.

2021 ◽  
Author(s):  
Norita Gildea ◽  
Adam McDermott ◽  
Joel Rocha ◽  
Donal O'Shea ◽  
Simon Green ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Time Course ◽  
Near Infrared ◽  
Vastus Lateralis ◽  
Moderate Intensity ◽  
Vastus Lateralis Muscle ◽  
Maximal Heart Rate ◽  
Continuous Training ◽  
Muscle Deoxygenation

We assessed the time course of changes in oxygen uptake (V̇O2) and muscle deoxygenation (i.e., deoxygenated haemoglobin and myoglobin, [HHb+Mb]) kinetics during transitions to moderate-intensity cycling following 12-weeks of low-volume high-intensity interval training (HIIT) vs. moderate-intensity continuous training (MICT) in adults with type 2 diabetes (T2D). Participants were randomly assigned to MICT (n=10, 50 min of moderate-intensity cycling), HIIT (n=9, 10x1 min at ~90% maximal heart rate) or non-exercising control (n=9) groups. Exercising groups trained 3 times per week and measurements were taken every 3 weeks. [HHb+Mb] kinetics were measured by near-infrared spectroscopy at the vastus lateralis muscle. The local matching of O2 delivery to O2 utilization was assessed by the Δ[HHb+Mb]/ΔV̇O2ratio. The pretraining time constant of the primary phase of V̇O2 (τV̇O2p ) decreased (P<0.05) at wk 3 of training in both MICT (from 44±12 to 32±5 s) and HIIT (from 42±8 to 32 ± 4 s) with no further changes thereafter; while no changes were reported in controls. The pretraining overall dynamic response of muscle deoxygenation (τ'[HHb+Mb]) was faster than τV̇O2p in all groups, resulting in Δ[HHb+Mb]/V̇O2p showing a transient "overshoot" relative to the subsequent steady-state level. After 3 wks, the Δ[HHb+Mb]/V̇O2p overshoot was eliminated only in the training groups, so that τ'[HHb+Mb] was not different to τV̇O2p in MICT and HIIT. The enhanced V̇O2 kinetics response consequent to both MICT and HIIT in T2D was likely attributed to a training-induced improvement in matching of O2 delivery to utilization.

scholarly journals Comparison of femoral blood gases and muscle near-infrared spectroscopy at exercise onset in humans

1999 ◽  
Vol 86 (2) ◽  
pp. 687-693 ◽  
Author(s):  
Maureen J. MacDonald ◽  
Mark A. Tarnopolsky ◽  
Howard J. Green ◽  
Richard L. Hughson
Keyword(s):  
Infrared Spectroscopy ◽  
Near Infrared Spectroscopy ◽  
Near Infrared ◽  
Vastus Lateralis ◽  
Femoral Vein ◽  
Blood Gases ◽  
Moderate Intensity ◽  
Reliable Estimate ◽  
Vastus Lateralis Muscle ◽  
Exercise Onset

We hypothesized that near-infrared spectroscopy (NIRS) measures of hemoglobin and/or myoglobin O2 saturation (IR-So 2) in the vascular bed of exercising muscle would parallel changes in femoral venous O2 saturation (S[Formula: see text]) at the onset of leg-kicking exercise in humans. Six healthy subjects performed transitions from rest to 48 ± 3 (SE)-W two-legged kicking exercise while breathing 14, 21, or 70% inspired O2. IR-So 2 was measured over the vastus lateralis muscle continuously during all tests, and femoral venous and radial artery blood samples were drawn simultaneously during rest and during 5 min of exercise. In all gas-breathing conditions, there was a rapid decrease in both IR-So 2 and SfvO2 at the onset of moderate-intensity leg-kicking exercise. Although SfvO2 remained at low levels throughout exercise, IR-So 2increased significantly after the first minute of exercise in both normoxia and hyperoxia. Contrary to the hypothesis, these data show that NIRS does not provide a reliable estimate of hemoglobin and/or O2 saturation as reflected by direct femoral vein sampling.

scholarly journals Near-Infrared Spectroscopy Is Promising to Detect Iliac Artery Flow Limitations in Athletes: A Pilot Study

2018 ◽  
Vol 2018 ◽  
pp. 1-11
Author(s):  
Martijn van Hooff ◽  
Goof Schep ◽  
Eduard Meijer ◽  
Mart Bender ◽  
Hans Savelberg
Keyword(s):  
Infrared Spectroscopy ◽  
Near Infrared Spectroscopy ◽  
Near Infrared ◽  
Vastus Lateralis ◽  
Diagnostic Techniques ◽  
Vastus Lateralis Muscle ◽  
Diagnostic Potential ◽  
Substantial Risk ◽  
Artery Flow ◽  
Healthy Participants

Endurance cyclists have a substantial risk to develop flow limitations in the iliac arteries during their career. These flow limitations are due to extreme hemodynamic stress which may result in functional arterial kinking and/or intravascular lesions. Early diagnosis may improve outcome and could prevent the necessity for surgical vascular repair. However, current diagnostic techniques have unsatisfactory sensitivity and cannot be applied during exercise. Near-infrared spectroscopy (NIRS) has shown great diagnostic potential in peripheral vascular disease and might bring a solution since it measures tissue oxygenation in real time during and after exercise. This report describes the first experiences of the application of NIRS in the vastus lateralis muscle during and after maximal graded cycling exercise in ten healthy participants and in three patients with flow limitations due to (1) subtle functional kinking, (2) an intravascular lesion, and (3) severe functional kinking. The results are put into perspective based on an empirically fitted model. Delayed recovery, showing clearly different types of patterns of tissue reoxygenation after exercise, was found in the affected athletes compared with the healthy participants. In the patients that had kinking of the arteries, tissue reoxygenation was clearly more delayed if NIRS was measured in provocative position with flexed hip. In this pilot experiment, clearly distinctive reoxygenation patterns are observed during recovery consistent with severity of flow limitation, indicating that NIRS is a promising diagnostic tool to detect and grade arterial flow limitations in athletes. Our findings may guide research and optimization of NIRS for future clinical application.

scholarly journals Suppression of cerebral hemodynamics is associated with reduced functional capacity in patients with heart failure

2011 ◽  
Vol 300 (4) ◽  
pp. H1545-H1555 ◽  
Author(s):  
Tieh-Cheng Fu ◽  
Chao-Hung Wang ◽  
Chih-Chin Hsu ◽  
Wen-Jin Cherng ◽  
Shu-Chun Huang ◽  
...  
Keyword(s):  
Heart Failure ◽  
Cardiac Output ◽  
Functional Capacity ◽  
Near Infrared ◽  
Vastus Lateralis ◽  
Functional Class ◽  
Vastus Lateralis Muscle ◽  
Functional Impairments ◽  
Patients With Heart Failure ◽  
Lateralis Muscle

This investigation elucidated the underlying mechanisms of functional impairments in patients with heart failure (HF) by simultaneously comparing cardiac-cerebral-muscle hemodynamic and ventilatory responses to exercise among HF patients with various functional capacities. One hundred one patients with HF [New York Heart Association HF functional class II (HF-II, n = 53) and functional class III (HF-III, n = 48) patients] and 71 normal subjects [older control (O-C, n = 39) and younger control (Y-C, n = 32) adults] performed an incremental exercise test using a bicycle ergometer. A recently developed noninvasive bioreactance device was adopted to measure cardiac hemodynamics, and near-infrared spectroscopy was employed to assess perfusions in the frontal cerebral lobe (Δ[THb]FC) and vastus lateralis muscle (Δ[THb]VL). The results demonstrated that the Y-C group had higher levels of cardiac output, Δ[THb]FC, and Δ[THb]VL during exercise than the O-C group. Moreover, these cardiac/peripheral hemodynamic responses to exercise in HF-III group were smaller than those in both HF-II and O-C groups. Although the change of cardiac output caused by exercise was normalized, the amounts of blood distributed to frontal cerebral lobe and vastus lateralis muscle in the HF-III group significantly declined during exercise. The HF-III patients had lower oxygen-uptake efficiency slopes (OUES) and greater V̇e-V̇o2 slopes than the HF-II patients and age-matched controls. However, neither hemodynamic nor ventilatory response to exercise differed significantly between the HF-II and O-C groups. Cardiac output, Δ[THb]FC, and Δ[THb]VL during exercise were directly related to the OUES and V̇o2peak and inversely related to the V̇e-V̇co2 slope. Moreover, cardiac output or Δ[THb]FC was an effect modifier, which modulated the correlation status between Δ[THb]VL and V̇e-V̇co2 slope. We concluded that the suppression of cerebral/muscle hemodynamics during exercise is associated with ventilatory abnormality, which reduces functional capacity in patients with HF.

Effects of acute hypoxia on cerebral and muscle oxygenation during incremental exercise

2007 ◽  
Vol 103 (1) ◽  
pp. 177-183 ◽  
Author(s):  
Andrew W. Subudhi ◽  
Andrew C. Dimmen ◽  
Robert C. Roach
Keyword(s):  
Power Output ◽  
Repeated Measures ◽  
Near Infrared ◽  
Cerebral Oxygenation ◽  
Vastus Lateralis ◽  
Acute Hypoxia ◽  
Incremental Exercise ◽  
Muscle Oxygenation ◽  
Peak Power Output ◽  
Vastus Lateralis Muscle

To determine if fatigue at maximal aerobic power output was associated with a critical decrease in cerebral oxygenation, 13 male cyclists performed incremental maximal exercise tests (25 W/min ramp) under normoxic (Norm: 21% FiO2) and acute hypoxic (Hypox: 12% FiO2) conditions. Near-infrared spectroscopy (NIRS) was used to monitor concentration (μM) changes of oxy- and deoxyhemoglobin (Δ[O2Hb], Δ[HHb]) in the left vastus lateralis muscle and frontal cerebral cortex. Changes in total Hb were calculated (Δ[THb] = Δ[O2Hb] + Δ[HHb]) and used as an index of change in regional blood volume. Repeated-measures ANOVA were performed across treatments and work rates (α = 0.05). During Norm, cerebral oxygenation rose between 25 and 75% peak power output {Powerpeak; increased (inc) Δ[O2Hb], inc. Δ[HHb], inc. Δ[THb]}, but fell from 75 to 100% Powerpeak {decreased (dec) Δ[O2Hb], inc. Δ[HHb], no change Δ[THb]}. In contrast, during Hypox, cerebral oxygenation dropped progressively across all work rates (dec. Δ[O2Hb], inc. Δ[HHb]), whereas Δ[THb] again rose up to 75% Powerpeak and remained constant thereafter. Changes in cerebral oxygenation during Hypox were larger than Norm. In muscle, oxygenation decreased progressively throughout exercise in both Norm and Hypox (dec. Δ[O2Hb], inc. Δ [HHb], inc. Δ[THb]), although Δ[O2Hb] was unchanged between 75 and 100% Powerpeak. Changes in muscle oxygenation were also greater in Hypox compared with Norm. On the basis of these findings, it is unlikely that changes in cerebral oxygenation limit incremental exercise performance in normoxia, yet it is possible that such changes play a more pivotal role in hypoxia.

Impaired cardiac reserve and severely diminished skeletal muscle O2 utilization mediate exercise intolerance in Barth syndrome

2011 ◽  
Vol 301 (5) ◽  
pp. H2122-H2129 ◽  
Author(s):  
Carolyn T. Spencer ◽  
Barry J. Byrne ◽  
Randall M. Bryant ◽  
Renee Margossian ◽  
Melissa Maisenbacher ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Mitochondrial Myopathy ◽  
Near Infrared ◽  
Vastus Lateralis ◽  
Cycle Ergometer ◽  
Barth Syndrome ◽  
Exercise Intolerance ◽  
Peak Exercise ◽  
Vastus Lateralis Muscle ◽  
And Control

Barth syndrome (BTHS) is a mitochondrial myopathy characterized by reports of exercise intolerance. We sought to determine if 1) BTHS leads to abnormalities of skeletal muscle O2 extraction/utilization and 2) exercise intolerance in BTHS is related to impaired O2 extraction/utilization, impaired cardiac function, or both. Participants with BTHS (age: 17 ± 5 yr, n = 15) and control participants (age: 13 ± 4 yr, n = 9) underwent graded exercise testing on a cycle ergometer with continuous ECG and metabolic measurements. Echocardiography was performed at rest and at peak exercise. Near-infrared spectroscopy of the vastus lateralis muscle was continuously recorded for measurements of skeletal muscle O2 extraction. Adjusting for age, peak O2 consumption (16.5 ± 4.0 vs. 39.5 ± 12.3 ml·kg−1·min−1, P < 0.001) and peak work rate (58 ± 19 vs. 166 ± 60 W, P < 0.001) were significantly lower in BTHS than control participants. The percent increase from rest to peak exercise in ejection fraction (BTHS: 3 ± 10 vs. control: 19 ± 4%, P < 0.01) was blunted in BTHS compared with control participants. The muscle tissue O2 saturation change from rest to peak exercise was paradoxically opposite (BTHS: 8 ± 16 vs. control: −5 ± 9, P < 0.01), and the deoxyhemoglobin change was blunted (BTHS: 0 ± 12 vs. control: 10 ± 8, P < 0.09) in BTHS compared with control participants, indicating impaired skeletal muscle extraction in BTHS. In conclusion, severe exercise intolerance in BTHS is due to both cardiac and skeletal muscle impairments that are consistent with cardiac and skeletal mitochondrial myopathy. These findings provide further insight to the pathophysiology of BTHS.

Cerebral desaturation during exercise reversed by O2 supplementation

1999 ◽  
Vol 277 (3) ◽  
pp. H1045-H1052 ◽  
Author(s):  
H. B. Nielsen ◽  
R. Boushel ◽  
P. Madsen ◽  
N. H. Secher
Keyword(s):  
Infrared Spectroscopy ◽  
Near Infrared Spectroscopy ◽  
Near Infrared ◽  
Cerebral Oxygenation ◽  
Vastus Lateralis ◽  
Work Capacity ◽  
Vastus Lateralis Muscle ◽  
Double Blind ◽  
Hemoglobin Saturation ◽  
Concentration Changes

The combined effects of hyperventilation and arterial desaturation on cerebral oxygenation ([Formula: see text]) were determined using near-infrared spectroscopy. Eleven competitive oarsmen were evaluated during a 6-min maximal ergometer row. The study was randomized in a double-blind fashion with an inspired O2 fraction of 0.21 or 0.30 in a crossover design. During exercise with an inspired O2 fraction of 0.21, the arterial CO2 pressure (35 ± 1 mmHg; mean ± SE) and O2 pressure (77 ± 2 mmHg) as well as the hemoglobin saturation (91.9 ± 0.7%) were reduced ( P < 0.05).[Formula: see text] was reduced from 80 ± 2 to 63 ± 2% ( P < 0.05), and the near-infrared spectroscopy-determined concentration changes in deoxy- (ΔHb) and oxyhemoglobin (ΔHbO2) of the vastus lateralis muscle increased 22 ± 3 μM and decreased 14 ± 3 μM, respectively ( P < 0.05). Increasing the inspired O2fraction to 0.30 did not affect ventilation (174 ± 4 l/min), but arterial CO2 pressure (37 ± 2 mmHg), O2 pressure (165 ± 5 mmHg), and hemoglobin O2saturation (99 ± 0.1%) increased ( P < 0.05).[Formula: see text] remained close to the resting level during exercise (79 ± 2 vs. 81 ± 2%), and although the muscle ΔHb (18 ± 2 μM) and ΔHbO2 (−12 ± 3 μM) were similar to those established without O2 supplementation, work capacity increased from 389 ± 11 to 413 ± 10 W ( P < 0.05). These results indicate that an elevated inspiratory O2fraction increases exercise performance related to maintained cerebral oxygenation rather than to an effect on the working muscles.

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