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Li SN, Peeling P, Scott BR, Peiffer JJ, Shaykevich A, Girard O. Maintenance of internal load despite a stepwise reduction in external load during moderate intensity heart rate clamped cycling with acute graded normobaric hypoxia in males. J Sci Med Sport 2023; 26:628-635. [PMID: 37852804 DOI: 10.1016/j.jsams.2023.09.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Revised: 09/07/2023] [Accepted: 09/11/2023] [Indexed: 10/20/2023]
Abstract
OBJECTIVES To investigate the acute effects of graded hypoxia on external and internal loads during 60 min of endurance cycling at a clamped heart rate. DESIGN Repeated measures. METHODS On separate visits, 16 trained males cycled for 60 min at a clamped heart rate corresponding to 80 % of their first ventilatory threshold at sea-level and 2500 m, 3000 m, 3500 m and 4000 m simulated altitudes (inspired oxygen fractions of 20.9 %, 15.4 %, 14.5 %, 13.6 % and 12.7 %, respectively). Markers of external (power output) and internal (blood lactate concentration, tissue saturation index, cardio-respiratory and perceptual responses) loads were measured every 15 min during cycling. Neuromuscular function of knee extensors was characterised pre- and post-exercise. RESULTS Compared to sea-level (101 ± 22 W), there was a stepwise reduction in power output with increasing hypoxia severity (-17.9 ± 8.9 %, -27.1 ± 10.7 %, -34.2 ± 12.0 % and - 44.6 ± 15.1 % at 2500 m, 3000 m, 3500 m, and 4000 m, respectively, all p < 0.05). Blood lactate and tissue saturation index were not different across hypoxia severities, and perceptual responses were exacerbated at 4000 m only, with increased breathing difficulty. Knee extensor torque decreased post-exercise (-14.5 ± 9.0 %, p < 0.05), independent of condition. CONCLUSIONS Increasing hypoxia severity reduces cycling power output and arterial oxygen saturation in a stepwise fashion without affecting exercise responses between sea-level and simulated altitudes up to 3500 m despite breathing difficulty being elevated at 4000 m.
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Affiliation(s)
- Siu Nam Li
- School of Human Sciences (Exercise and Sports Science), The University of Western Australia, Australia.
| | - Peter Peeling
- School of Human Sciences (Exercise and Sports Science), The University of Western Australia, Australia; Department of Sport Science, Western Australian Institute of Sport, Australia
| | - Brendan R Scott
- Murdoch Applied Sport Science Laboratory, Discipline of Exercise Science, Murdoch University, Australia; Centre for Healthy Ageing, Murdoch University, Australia
| | - Jeremiah J Peiffer
- Murdoch Applied Sport Science Laboratory, Discipline of Exercise Science, Murdoch University, Australia; Centre for Healthy Ageing, Murdoch University, Australia
| | - Alex Shaykevich
- School of Human Sciences (Exercise and Sports Science), The University of Western Australia, Australia; Perron Institute for Neurological and Translational Science, Australia
| | - Olivier Girard
- School of Human Sciences (Exercise and Sports Science), The University of Western Australia, Australia.
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Al-Samir S, Yildirim AÖ, Sidhaye VK, King LS, Breves G, Conlon TM, Stoeger C, Gailus-Durner V, Fuchs H, Hrabé de Angelis M, Gros G, Endeward V. Aqp5 -/- mice exhibit reduced maximal body O 2 consumption under cold exposure, normal pulmonary gas exchange, and impaired formation of brown adipose tissue. Am J Physiol Regul Integr Comp Physiol 2023; 324:R109-R119. [PMID: 36409022 DOI: 10.1152/ajpregu.00130.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The fundamental body functions that determine maximal O2 uptake (V̇o2max) have not been studied in Aqp5-/- mice (aquaporin 5, AQP5). We measured V̇o2max to globally assess these functions and then investigated why it was found altered in Aqp5-/- mice. V̇o2max was measured by the Helox technique, which elicits maximal metabolic rate by intense cold exposure of the animals. We found V̇o2max reduced in Aqp5-/- mice by 20%-30% compared with wild-type (WT) mice. As AQP5 has been implicated to act as a membrane channel for respiratory gases, we studied whether this is caused by the known lack of AQP5 in the alveolar epithelial membranes of Aqp5-/- mice. Lung function parameters as well as arterial O2 saturation were normal and identical between Aqp5-/- and WT mice, indicating that AQP5 does not contribute to pulmonary O2 exchange. The cause for the decreased V̇o2max thus might be found in decreased O2 consumption of an intensely O2-consuming peripheral organ such as activated brown adipose tissue (BAT). We found indeed that absence of AQP5 greatly reduces the amount of interscapular BAT formed in response to 4 wk of cold exposure, from 63% in WT to 25% in Aqp5-/- animals. We conclude that lack of AQP5 does not affect pulmonary O2 exchange, but greatly inhibits transformation of white to brown adipose tissue. As under cold exposure, BAT is a major source of the animals' heat production, reduction of BAT likely causes the decrease in V̇o2max under this condition.
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Affiliation(s)
- Samer Al-Samir
- Zentrum Physiologie, AG Vegetative Physiologie, Medizinische Hochschule, Hannover, Germany
| | - Ali Önder Yildirim
- Comprehensive Pneumology Center, Institute of Lung Biology and Disease, Helmholtz Zentrum München, Member of the German Center for Lung Research (DZL), München, Germany
| | - Venkataramana K Sidhaye
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins School of Medicine, Baltimore, Maryland
| | - Landon S King
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins School of Medicine, Baltimore, Maryland
| | - Gerhard Breves
- Institut für Physiologie und Zellbiologie, Tierärztliche Hochschule Hannover, Hannover, Germany
| | - Thomas M Conlon
- Comprehensive Pneumology Center, Institute of Lung Biology and Disease, Helmholtz Zentrum München, Member of the German Center for Lung Research (DZL), München, Germany
| | - Claudia Stoeger
- Institute of Experimental Genetics, German Mouse Clinic, Helmholtz Zentrum München, German Research Center for Environmental Health, GmbH, Neuherberg, Germany
| | - Valerie Gailus-Durner
- Institute of Experimental Genetics, German Mouse Clinic, Helmholtz Zentrum München, German Research Center for Environmental Health, GmbH, Neuherberg, Germany
| | - Helmut Fuchs
- Institute of Experimental Genetics, German Mouse Clinic, Helmholtz Zentrum München, German Research Center for Environmental Health, GmbH, Neuherberg, Germany
| | - Martin Hrabé de Angelis
- Institute of Experimental Genetics, German Mouse Clinic, Helmholtz Zentrum München, German Research Center for Environmental Health, GmbH, Neuherberg, Germany.,German Center for Diabetes Research, Neuherberg, Germany.,Chair of Experimental Genetics, Technische Universität München School of Life Sciences, Technische Universität München, Freising, Germany
| | - Gerolf Gros
- Zentrum Physiologie, AG Vegetative Physiologie, Medizinische Hochschule, Hannover, Germany
| | - Volker Endeward
- Zentrum Physiologie, AG Vegetative Physiologie, Medizinische Hochschule, Hannover, Germany
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Li Y, Li J, Atakan MM, Wang Z, Hu Y, Nazif M, Zarekookandeh N, Ye HZ, Kuang J, Ferri A, Petersen A, Garnham A, Bishop DJ, Girard O, Huang Y, Yan X. Methods to match high-intensity interval exercise intensity in hypoxia and normoxia - A pilot study. J Exerc Sci Fit 2022; 20:70-76. [PMID: 35024050 PMCID: PMC8728434 DOI: 10.1016/j.jesf.2021.12.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Revised: 12/20/2021] [Accepted: 12/22/2021] [Indexed: 12/30/2022] Open
Abstract
The aim of this study was to compare high-intensity interval exercise (HIIE) sessions prescribed on the basis of a maximal value (peak power output, PPO) and a submaximal value (lactate threshold, LT) derived from graded exercise tests (GXTs) in normoxia and hypoxia. Methods: A total of ten males (aged 18–37) volunteered to participate in this study. The experimental protocol consisted of a familiarization procedure, two GXTs under normoxia (FiO2 = 0.209) and two GXTs under normobaric hypoxia (FiO2 = 0.140), and three HIIE sessions performed in a random order. The HIIE sessions included one at hypoxia (HY) and two at normoxia (one matched for the absolute intensity in hypoxia, designated as NA, and one matched for the relative intensity in hypoxia, designated as NR). Results: The data demonstrated that there was significant lower peak oxygen uptake (V̇O2peak), peak heart rate (HRpeak), PPO, and LT derived from GXTs in hypoxia, with higher respiratory exchange ratio (RER), when compared to those from GXTs performed in normoxia (p < 0.001). Among the three HIIE sessions, the NA session resulted in lower percentage of HRpeak (85.0 ± 7.5% vs 94.4 ± 5.0%; p = 0.002) and V̇O2peak (74.1 ± 9.1% vs 88.7 ± 7.7%; p = 0.005), when compared to the NR session. HIIE sessions in HY and NR resulted in similar percentage of HRpeak and V̇O2peak, as well as similar rating of perceived exertion and RER. The blood lactate level increased immediately after all the three HIIE sessions (p < 0.001), while higher blood lactate concentrations were observed immediately after the HY (p = 0.0003) and NR (p = 0.014) sessions when compared with NA. Conclusion: Combining of PPO and LT derived from GXTs can be used to prescribe exercise intensity of HIIE in hypoxia.
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Affiliation(s)
- Yanchun Li
- China Institute of Sport and Health Science, Beijing Sport University, Beijing, 100084, China
| | - Jia Li
- Institute for Health and Sport,(iHeS), Victoria University, Melbourne, 3011, Australia.,College of Physical Education, Southwest University, Chongqin, China
| | - Muhammed M Atakan
- Institute for Health and Sport,(iHeS), Victoria University, Melbourne, 3011, Australia.,Division of Exercise Nutrition and Metabolism, Faculty of Sport Sciences, Hacettepe University, Ankara, 06800, Turkey
| | - Zhenhuan Wang
- Institute for Health and Sport,(iHeS), Victoria University, Melbourne, 3011, Australia
| | - Yang Hu
- China Institute of Sport and Health Science, Beijing Sport University, Beijing, 100084, China
| | - Mostafa Nazif
- Institute for Health and Sport,(iHeS), Victoria University, Melbourne, 3011, Australia
| | - Navabeh Zarekookandeh
- Institute for Health and Sport,(iHeS), Victoria University, Melbourne, 3011, Australia
| | - Henry Zhihong Ye
- School of Biological Sciences, Monash University, Melbourne, 3800, Australia
| | - Jujiao Kuang
- Institute for Health and Sport,(iHeS), Victoria University, Melbourne, 3011, Australia.,Sarcopenia Research Program, Australia Institute for Musculoskeletal Sciences (AIMSS), Melbourne, 3021, Australia
| | - Alessandra Ferri
- Institute for Health and Sport,(iHeS), Victoria University, Melbourne, 3011, Australia
| | - Aaron Petersen
- Institute for Health and Sport,(iHeS), Victoria University, Melbourne, 3011, Australia
| | - Andrew Garnham
- Institute for Health and Sport,(iHeS), Victoria University, Melbourne, 3011, Australia
| | - David J Bishop
- Institute for Health and Sport,(iHeS), Victoria University, Melbourne, 3011, Australia
| | - Olivier Girard
- School of Human Sciences, The University of Western Australia, Perth, 6009, Australia
| | - Yaru Huang
- Department of Physical Education and Art, China Agricultural University, Beijing, 100083, China
| | - Xu Yan
- Institute for Health and Sport,(iHeS), Victoria University, Melbourne, 3011, Australia.,Sarcopenia Research Program, Australia Institute for Musculoskeletal Sciences (AIMSS), Melbourne, 3021, Australia.,Department of Medicine - Western Health, The University of Melbourne, Melbourne, 3021, Australia
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Grossman KJ, Lim DJ, Murias JM, Belfry GR. The Effect of Breathing Patterns Common to Competitive Swimming on Gas Exchange and Muscle Deoxygenation During Heavy-Intensity Fartlek Exercise. Front Physiol 2021; 12:723951. [PMID: 34899369 PMCID: PMC8652135 DOI: 10.3389/fphys.2021.723951] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 10/14/2021] [Indexed: 11/29/2022] Open
Abstract
During competitive freestyle swimming, the change of direction requires a turn followed by ∼15 m of underwater kicking at various intensities that require a ∼5 s breath-hold (BH). Upon surfacing, breathing must be regulated, as head rotation is necessary to facilitate the breath while completing the length of the pool (∼25 s). This study compared the respiratory and muscle deoxygenation responses of regulated breathing vs. free breathing, during these 25–5 s cycles. It was hypothesized that with the addition of a BH and sprint during heavy-intensity (HVY) exercise, oxygen uptake (VO2) and oxygen saturation (SatO2) would decrease, and muscle deoxygenation ([HHb]) and total hemoglobin ([Hbtot]) would increase. Ten healthy male participants (24 ± 3 years) performed 4–6 min trials of HVY cycling in the following conditions: (1) continuous free breathing (CONLD); (2) continuous with 5 s BH every 25 s (CONLD-BH); (3) Fartlek (FLK), a 5 s sprint followed by 25 s of HVY; and (4) a combined Fartlek and BH (FLK-BH). Continuous collection of VO2 and SatO2, [Hbtot], and [HHb] via breath-by-breath gas analysis and near-infrared spectroscopy (normalized to baseline) was performed. Breathing frequency and tidal volumes were matched between CONLD and CONLD-BH and between FLK and FLK-BH. As a result, VO2 was unchanged between CONLD (2.12 ± 0.35 L/min) and CONLD-BH (2.15 ± 0.42 L/min; p = 0.116) and between FLK (2.24 ± 0.40 L/min) and FLK-BH (2.20 ± 0.45 L/min; p = 0.861). SatO2 was higher in CONLD (63 ± 1.9%) than CONLD-BH (59 ± 3.3%; p < 0.001), but was unchanged between FLK (61 ± 2.2%) and FLK-BH (62 ± 3.1%; p = 0.462). Δ[Hbtot] is higher in CONLD (3.3 ± 1.6 μM) than CONLD-BH (-2.5 ± 1.2 μM; Δ177%; p < 0.001), but was unchanged between FLK (2.0 ± 1.6 μM) and FLK-BH (0.82 ± 1.4 μM; p = 0.979). Δ[HHb] was higher in CONLD (7.3 ± 1.8μM) than CONLD-BH (7.0 ± 2.0μM; Δ4%; p = 0.011) and lower in FLK (6.7 ± 1.8μM) compared to FLK-BH (8.7 ± 2.4 μM; p < 0.001). It is suggested that the unchanged VO2 between CONLD and CONLD-BH was supported by increased deoxygenation as reflected by decreased Δ[Hbtot] and blunted Δ[HHb], via apneic-driven redistribution of blood flow away from working muscles, which was reflected by the decreased SatO2. However, the preserved VO2 during FLK-BH vs. FLK has been underpinned by an increase in [HHb].
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Affiliation(s)
- Kevin J Grossman
- School of Kinesiology, The University of Western Ontario, London, ON, Canada
| | - David J Lim
- School of Kinesiology, The University of Western Ontario, London, ON, Canada
| | - Juan M Murias
- Faculty of Kinesiology, University of Calgary, Calgary, ON, Canada
| | - Glen R Belfry
- School of Kinesiology, The University of Western Ontario, London, ON, Canada
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Dans PW, Foglia SD, Nelson AJ. Data Processing in Functional Near-Infrared Spectroscopy (fNIRS) Motor Control Research. Brain Sci 2021; 11:606. [PMID: 34065136 PMCID: PMC8151801 DOI: 10.3390/brainsci11050606] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 05/05/2021] [Accepted: 05/07/2021] [Indexed: 12/26/2022] Open
Abstract
FNIRS pre-processing and processing methodologies are very important-how a researcher chooses to process their data can change the outcome of an experiment. The purpose of this review is to provide a guide on fNIRS pre-processing and processing techniques pertinent to the field of human motor control research. One hundred and twenty-three articles were selected from the motor control field and were examined on the basis of their fNIRS pre-processing and processing methodologies. Information was gathered about the most frequently used techniques in the field, which included frequency cutoff filters, wavelet filters, smoothing filters, and the general linear model (GLM). We discuss the methodologies of and considerations for these frequently used techniques, as well as those for some alternative techniques. Additionally, general considerations for processing are discussed.
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Affiliation(s)
- Patrick W. Dans
- Department of Kinesiology, McMaster University, Hamilton, ON L8S 4K1, Canada;
| | - Stevie D. Foglia
- School of Biomedical Engineering, McMaster University, Hamilton, ON L8S 4K1, Canada;
| | - Aimee J. Nelson
- Department of Kinesiology, McMaster University, Hamilton, ON L8S 4K1, Canada;
- School of Biomedical Engineering, McMaster University, Hamilton, ON L8S 4K1, Canada;
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Post-exercise cardiac autonomic and cardiovascular responses to heart rate-matched and work rate-matched hypoxic exercise. Eur J Appl Physiol 2021; 121:2061-2076. [PMID: 33811558 PMCID: PMC8192382 DOI: 10.1007/s00421-021-04678-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Accepted: 03/28/2021] [Indexed: 12/30/2022]
Abstract
Purpose This study investigated the effect of performing hypoxic exercise at the same heart rate (HR) or work rate (WR) as normoxic exercise on post-exercise autonomic and cardiovascular responses. Methods Thirteen men performed three interval-type exercise sessions (5 × 5-min; 1-min recovery): normoxic exercise at 80% of the WR at the first ventilatory threshold (N), hypoxic exercise (FiO2 = 14.2%) at the same WR as N (H-WR) and hypoxic exercise at the same HR as N (H-HR). Autonomic and cardiovascular assessments were conducted before and after exercise, both at rest and during active squat–stand manoeuvres (SS). Results Compared to N, H-WR elicited a higher HR response (≈ 83% vs ≈ 75%HRmax, p < 0.001) and H-HR a reduced exercise WR (− 21.1 ± 9.3%, p < 0.001). Cardiac parasympathetic indices were reduced 15 min after exercise and recovered within 60 min in N and H-HR, but not after H-WR (p < 0.05). H-WR altered cardiac baroreflex sensitivity (cBRS) both at rest and during SS (specifically in the control of blood pressure fall during standing phases) in the first 60 min after the exercise bout (p < 0.05). Post-exercise hypotension (PEH) did not occur in H-HR (p > 0.05) but lasted longer in H-WR than in N (p < 0.05). Conclusions Moderate HR-matched hypoxic exercise mimicked post-exercise autonomic responses of normoxic exercise without resulting in significant PEH. This may relate to the reduced WR and the limited associated mechanical/metabolic strain. Conversely, WR-matched hypoxic exercise impacted upon post-exercise autonomic and cardiovascular responses, delaying cardiac autonomic recovery, temporarily decreasing cBRS and evoking prolonged PEH. Supplementary Information The online version contains supplementary material available at 10.1007/s00421-021-04678-5.
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Hobbins L, Girard O, Gaoua N, Hunter S. Acute psycho-physiological responses to perceptually regulated hypoxic and normoxic interval walks in overweight-to-obese adults. J Sci Med Sport 2020; 24:481-487. [PMID: 33281095 DOI: 10.1016/j.jsams.2020.11.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Revised: 10/02/2020] [Accepted: 11/16/2020] [Indexed: 12/18/2022]
Abstract
OBJECTIVES We investigated psycho-physiological responses to perceptually regulated interval walks in hypoxia versus normoxia in obese individuals. DESIGN Within-participants repeated measures. METHODS Ten obese adults (BMI=32±3kg/m-2) completed a 60-min interval session (15×2min walking at a rating of perceived exertion of 14 on the 6-20 Borg scale with 2min of rest) either in hypoxia (FiO2=13.0%, HYP) or normoxia (NOR). A third trial replicating the HYP speed pattern was carried out in normoxia as a control (CON). Exercise responses were analysed comparing the average of 1st to 3rd exercise bouts to those of the 4th-6th, 7th-9th, 10th-12th and 13th-15th exercise bouts (block 1 versus 2, 3, 4 and 5). RESULTS Treadmill speed was slower during block 4 (6.14±0.67 versus 6.24±0.73km/h-1) and block 5 (6.12±0.64 versus 6.25±0.75km/h-1) in HYP compared to NOR or CON (p=0.009). Compared to NOR and CON, heart rate was +6-10% higher (p=0.001), whilst arterial oxygen saturation (-12-13%) was lower (p<0.001) in HYP. Perceived limb discomfort was lower in HYP and CON versus NOR (-21±4% and -34±6%; p=0.004). CONCLUSIONS In overweight-to-obese adults, perceptually regulated interval walks in hypoxia versus normoxia leads to progressively slower speeds along with lower limb discomfort and larger physiological stress than normoxia. Walking at the speed adopted in hypoxia produces similar psycho-physiological responses at the same absolute intensity in normoxia.
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Affiliation(s)
- Liam Hobbins
- Sport and Exercise Science Research Centre (SESRC), London South Bank University, United Kingdom
| | - Olivier Girard
- School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Australia.
| | - Nadia Gaoua
- Sport and Exercise Science Research Centre (SESRC), London South Bank University, United Kingdom
| | - Steve Hunter
- Sport and Exercise Science Research Centre (SESRC), London South Bank University, United Kingdom
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Li SN, Hobbins L, Morin JB, Ryu JH, Gaoua N, Hunter S, Girard O. Running mechanics adjustments to perceptually-regulated interval runs in hypoxia and normoxia. J Sci Med Sport 2020; 23:1111-1116. [DOI: 10.1016/j.jsams.2020.04.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Revised: 03/18/2020] [Accepted: 04/03/2020] [Indexed: 01/03/2023]
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Ušaj A, Mekjavic IB, Kapus J, McDonnell AC, Jaki Mekjavic P, Debevec T. Muscle Oxygenation During Hypoxic Exercise in Children and Adults. Front Physiol 2019; 10:1385. [PMID: 31787903 PMCID: PMC6854007 DOI: 10.3389/fphys.2019.01385] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Accepted: 10/21/2019] [Indexed: 12/31/2022] Open
Abstract
INTRODUCTION While hypoxia is known to decrease peak oxygen uptake ( V . o 2 max) and maximal power output in both adults and children its influence on submaximal exercise cardiorespiratory and, especially, muscle oxygenation responses remains unclear. METHODS Eight pre-pubertal boys (age = 8 ± 2 years.; body mass (BM) = 29 ± 7 kg) and seven adult males (age = 39 ± 4 years.; BM = 80 ± 8 kg) underwent graded exercise tests in both normoxic (PiO2 = 134 ± 0.4 mmHg) and hypoxic (PiO2 = 105 ± 0.6 mmHg) condition. Continuous breath-by-breath gas exchange and near infrared spectroscopy measurements, to assess the vastus lateralis oxygenation, were performed during both tests. The gas exchange threshold (GET) and muscle oxygenation thresholds were subsequently determined for both groups in both conditions. RESULTS In both groups, hypoxia did not significantly alter either GET or the corresponding V . o 2 at GET. In adults, higher V . E levels were observed in hypoxia (45 ± 6 l/min) compared to normoxia (36 ± 6 l/min, p < 0.05) at intensities above GET. In contrast, in children both the hypoxic V . E and V . o 2 responses were significantly greater than those observed in normoxia only at intensities below GET (p < 0.01 for V . E and p < 0.05 for V . o 2). Higher exercise-related heart rate (HR) levels in hypoxia, compared to normoxia, were only noted in adults (p < 0.01). Interestingly, hypoxia per se did not influence the muscle oxygenation thresholds during exercise in neither group. However, and in contrast to adults, the children exhibited significantly higher total hemoglobin concentration during hypoxic as compared to normoxic exercise (tHb) at lower exercise intensities (30 and 60 W, p = 0.01). CONCLUSION These results suggest that in adults, hypoxia augments exercise ventilation at intensities above GET and might also maintain muscle blood oxygenation via increased HR. On the other hand, children exhibit a greater change of muscle blood perfusion, oxygen uptake as well as ventilation at exercise intensities below GET.
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Affiliation(s)
- Anton Ušaj
- Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia
| | - Igor B Mekjavic
- Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia.,Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Jernej Kapus
- Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia
| | - Adam C McDonnell
- Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia
| | | | - Tadej Debevec
- Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia.,Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia
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