ECSS Paris 2023: OP-PN16
INTRODUCTION: The heterogeneity of the effects of acute hypoxia on substrate oxidation during exercise matched for relative intensity compared with normoxia (N) has been previously reported [1]. While fat oxidation kinetics over a wide range of intensities in N has already been well described [2, 3], the homologous kinetics in normobaric hypoxia (NH) and its comparison at identical relative intensities with N are unknown. Therefore, this study aimed to investigate the effect of acute NH vs. N on whole-body fat oxidation kinetics at identical relative intensities during a submaximal graded cycling test. METHODS: Thirteen active men (24.9±3.0 yrs) performed i) two maximal incremental cycling tests to determine maximal oxygen uptake (VO2max) in either NH [hypoxic chamber; inspired fraction of oxygen (FiO2) = 12.7%, ~4000 m] or N [FiO2 = 20.7%, ~375 m], and ii) two submaximal graded cycling tests to assess whole-body fat oxidation in each condition, using indirect calorimetry after an overnight fast and 20-min acclimation to NH. A sinusoidal model was used to characterize, with three independent parameters (dilatation, symmetry and translation), the whole-body fat oxidation kinetics and to determine Fatmax [i.e., the intensity eliciting the maximal fat oxidation (MFO)] in both conditions [2]. RESULTS: VO2max was significantly lower (50.4±5.3 vs. 61.5±7.5 ml/kg/min, p<0.001) and Fatmax was significantly higher (63.9±6.7 vs. 57.7±4.3 %VO2max, p<0.001) in NH vs. N. MFO (0.66±0.22 vs. 0.49±0.12 g/min, p=0.005) and whole-body fat oxidation rates for exercise intensities ranging from 50 to 85% VO2max (p<0.019) were significantly higher in NH vs. N. The mean kinetics in NH was characterized by a significantly greater dilatation (widening of the curve, p=0.01) with no significant difference for symmetry (p=0.17) and translation (p=0.79) vs. N. CONCLUSION: Whole-body fat oxidation kinetics differed between normobaric hypoxia and normoxia when compared at the same relative exercise intensities, with greater dilatation, MFO, Fatmax and fat oxidation rates during moderate- and high-intensity exercises in normobaric hypoxia. Exercise intensity may thus play a central role in the effect of hypoxia on fat oxidation, confirming previous findings involving carbohydrate intake [4]. For the same relative moderate- to high-intensity exercise, the greater reliance on fat oxidation in normobaric hypoxia vs. normoxia seems consistent with the increased oxidation of plasma non-esterified fatty acids, representing a more important part of total fat oxidation during moderate- to high-intensity exercise. The present findings support that acute exposure to normobaric hypoxia vs. normoxia after overnight fasting enhances the metabolic pathways of fat oxidation during moderate- to high-intensity exercise. REFERENCES: [1] Griffiths, J Int Soc Sports Nutr, 2019 [2] Cheneviere, Med Sci Sports Exerc, 2009 [3] Jeukendrup and Wallis, Int J Sports Med, 2005 [4] O’Hara et al., Physiol Rep, 2017
Read CV Johan GarciaECSS Paris 2023: OP-PN16
INTRODUCTION: The association between cerebral oxygen level and cognitive function is extensively documented in the normal oxygen range. However, the heterogeneity in protocols designed to investigate the impact of hypoxia-induced changes in cognitive function prevents definitive conclusions regarding underlying mechanisms of cognitive performance. In this study, we aimed to assess the effect of acute normobaric hypoxic conditions on cognitive functions and cerebral oxygenation. METHODS: We enrolled healthy participants aged 18 to 30 in a crossover study to explore the effects of 4 simulated altitudes on executive function. These altitudes included normoxia at sea level (SL; FiO2: 21%), low hypoxia (1600 m altitude; FiO2:17.2%), moderate hypoxia (3000 m altitude; FiO2:14.4%), and high hypoxia (4100 m altitude; FiO2:12.5%). Executive function was assessed using 4 standardized cognitive tasks: Stroop task, N-Back, Corsi blocks, and Go/No-Go. The sequence of cognitive tasks and altitude conditions were randomized. Peripheral oxygen saturation (SpO2) and heart rate (HR) were continuously monitored. Cerebral oxygenation was measured using near-infrared spectroscopy during each condition. Changes in the tissue saturation index (ΔTSI%), total hemoglobin (ΔtHb), deoxyhemoglobin (ΔHHb), and oxyhemoglobin (ΔO2Hb) were defined as the difference between each hypoxia level and the normoxia resting state. Perceived exertion after each task was assessed using the DP15 rating scale. RESULTS: In 23 participants (22.2±2.8 years; 11 females and 12 males), SpO2 decreased with increasing hypoxia dose, and each condition was different from the others (p<0.001). There was a significant association between perceived exertion level after the Stroop task and hypoxic level (p=0.003) but not after the other 3 cognitive tasks (p=0.098 to 0.977). The hypoxia was only statistically associated with accuracy during the Stroop task (the higher the hypoxia, the higher the mean error rate during the task; p=0.039) but not with other tasks. No significant change in tissue saturation and total hemoglobin (ΔTSI% and (ΔtHb) were found. However, there was a statistically significant increase in deoxyhemoglobin values (ΔHHb) and a significant decrease in oxyhemoglobin (ΔO2Hb) for every cognitive task with the severity of hypoxia. CONCLUSION: In summary, our findings suggest that only severe acute normobaric hypoxia impacts executive functions in young healthy subjects. This modest effect may be partially due to compensatory mechanisms operating at the cerebral oxygen extraction level. Nevertheless, participants reported a progressively increased in the perception of task difficulty under all progressive hypoxia levels during every demanding task suggesting a larger cognitive cost.
Read CV Corentin FaucherECSS Paris 2023: OP-PN16
INTRODUCTION: Acute exercise under hypoxic conditions induces a drop in blood oxygen levels (hypoxemia) and impact in continuous oxygen supply to tissues (1). Terrestrial altitude presents a logistical challenge. For this reason, certain research endeavours to replicate high-altitude scenarios within normobaric hypoxia (NH) (2). However, one of the main concerns in using NH systems is the accumulation of CO2 levels and increased temperature and humidity inside the tent resulting from athletes’ exhalation (3). Therefore, combining reduced oxygen availability and increased environmental stressors could affect performance (4). The present study aims to analyse the effects of a resistance training (RT) period under two different NH environment emplacements on strength development. METHODS: Nineteen men (22,16 ± 2,94 years; 176,79 ± 7,47 cm; 76,32 ± 11,00 kg) participated in an 8-week- hypertrophy RT program (3 sessions /week) under systemic moderate NH (FiO2 = 15,9%) in a tent (8 m2; 50 l/min/persona) or in a room (60 m2; 900 l/min/persona). Before and after the program, one repetition maximum (1RM) in back squat and bench press exercises were evaluated. Maximal blood lactate and rating of perceived exertion (RPE min25) were also measured after the programs first and last sessions. Environmental CO2 was monitored during the RT sessions. RESULTS: The values of change in CO2 concentration from the beginning to the end of the session were significantly higher in the tent (4947,70 ± 1918,84 ppm) compared with the room (550,31 ± 405,40 ppm). 1RM increased in both groups (p < 0.05), with no differences between groups (p > 0.05). No differences were found in the RPE and lactate between conditions (p > 0.05). CONCLUSION: Results reveal a strength development after a RT period in NH regardless of the environmental additional stressors. However, such a higher CO2 concentration measured in the NH tent could lead to a greater physiological strain during exercise, impacting the normal functioning of organic systems not evaluated in this study. Therefore, the type of equipment used must be considered when conducting NH training. References: 1. Billaut F., et al. PLoS ONE. 2013;8: e77297. 2. Coppel J., et al. Extrem Physiol Med. 2015;4(1). 3. Vasquez-Bonilla AA., et al. J Clin Med. 2021; 22;10(21):4879. 4. Girard O., et al Front. Sports Act. Living. 2020; 2:26. Funding: This research was funded by the Spanish Ministry of Science, Innovation and Universities under grant number PGC2018-097388-B-I00 and by the Andalusian FEDER Operational Program under grants number A-SEJ-246-UGR18 & B-CTS-374-UGR20.
Read CV JUAN ABRIL JIMÉNEZECSS Paris 2023: OP-PN16