Mechanical, Cardiorespiratory, and Muscular Oxygenation Responses to Sprint Interval Exercises Under Different Hypoxic Conditions in Healthy Moderately Trained Men.

Objective: The aim of this study was to determine the effects of sprint interval exercises (SIT) conducted under different conditions (hypoxia and blood flow restriction [BFR]) on mechanical, cardiorespiratory, and muscular O <sub>2</sub> extraction responses. Methods: For this purpose, 13 healthy moderately trained men completed five bouts of 30 s all-out exercises interspaced by 4 min resting periods with lower limb bilateral BFR at 60% of the femoral artery occlusive pressure (BFR <sub>60</sub> ) during the first 2 min of recovery, with gravity-induced BFR (pedaling in supine position; G-BFR), in a hypoxic chamber (FiO <sub>2</sub> ≈13%; HYP) or without additional stress (NOR). Peak and average power, time to achieve peak power, rating of perceived exertion (RPE), and a fatigue index (FI) were analyzed. Gas exchanges and muscular oxygenation were measured by metabolic cart and NIRS, respectively. Heart rate (HR) and peripheral oxygen saturation (SpO <sub>2</sub> ) were continuously recorded. Results: Regarding mechanical responses, peak and average power decreased after each sprint (p < 0.001) excepting between sprints four and five. Time to reach peak power increased between the three first sprints and sprint number five (p < 0.001). RPE increased throughout the exercises (p < 0.001). Of note, peak and average power, time to achieve peak power and RPE were lower in G-BFR (p < 0.001). Results also showed that SpO <sub>2</sub> decreased in the last sprints for all the conditions and was lower for HYP (p < 0.001). In addition, Δ[O <sub>2</sub> Hb] increased in the last two sprints (p < 0.001). Concerning cardiorespiratory parameters, BFR <sub>60</sub> application induced a decrease in gas exchange rates, which increased after its release compared to the other conditions (p < 0.001). Moreover, muscle blood concentration was higher for BFR <sub>60</sub> (p < 0.001). Importantly, average and peak oxygen consumption and muscular oxyhemoglobin availability during sprints decreased for HYP (p < 0.001). Finally, the tissue saturation index was lower in G-BFR. Conclusions: Thus, SIT associated with G-BFR displayed lower mechanical, cardiorespiratory responses, and skeletal muscle oxygenation than the other conditions. Exercise with BFR <sub>60</sub> promotes higher blood accumulation within working muscles, suggesting that BFR <sub>60</sub> may additionally affect cellular stress. In addition, HYP and G-BFR induced local hypoxia with higher levels for G-BFR when considering both exercise bouts and recovery periods

Effects of intermittent hypoxic training performed at high hypoxia level on exercise performance in highly trained runners.

This study exanimated the effects of intermittent hypoxic training (IHT) conducted at a high level of hypoxia with recovery at ambient air on aerobic/anaerobic capacities at sea level and hematological variations. According to a double-blind randomized design, fifteen highly endurance-trained runners completed a 6-weeks regimented training with 3 sessions per week consisting of intermittent runs (6x work-rest ratio of 5':5') on a treadmill at 80-85% of maximal aerobic speed ([Formula: see text]). Nine athletes (hypoxic group, HG) performed the exercise bouts at FI0 <sub>2</sub>  = 10.6-11.4% while six athletes (normoxic group, NG) exercised at ambient air. Running time to exhaustion at a velocity corresponding to 95% [Formula: see text] significantly increased for HG while no effect was found for NG. Regarding [Formula: see text], no significant effects were found in either training group. In addition, the decline of jumping performances over a 45s-continuous maximal vertical jump test (i.e. anaerobic capacity index) tended to be lower in HG compared to NG. The levels of the studied hematological variables, including erythropoietin and hematocrit, did not significantly change for either HG or NG. These results highlight that our IHT protocol may induce additional effects on aerobic performance without compromising the anaerobic capacity index in highly-trained athletes

Effects of Blood Flow Restriction on O₂ Muscle Extraction and O₂ Pulmonary Uptake Kinetics During Heavy Exercise.

This study aimed to determine the effects of three levels of blood flow restriction (BFR) on and O <sub>2</sub> extraction kinetics during heavy cycling exercise transitions. Twelve healthy trained males completed two bouts of 10 min heavy intensity exercise without BFR (CON), with 40% or 50% BFR (BFR40 and BFR50, respectively). and tissue saturation index (TSI) were continuously measured and modelled using multiexponential functions. The time constant of the primary phase was significantly slowed in BFR40 (26.4 ± 2.0s; p < 0.001) and BFR50 (27.1 ± 2.1s; p = 0.001) compared to CON (19.0 ± 1.1s). The amplitude of the slow component was significantly increased (p < 0.001) with BFR in a pressure-dependent manner 3.6 ± 0.7, 6.7 ± 0.9 and 9.7 ± 1.0 ml·min <sup>-1</sup> ·kg <sup>-1</sup> for CON, BFR40, and BFR50, respectively. While no acceleration of the primary component of the TSI kinetics was observed, there was an increase (p < 0.001) of the phase 3 amplitude with BFR (CON -0.8 ± 0.3% VS BFR40 -2.9 ± 0.9%, CON VS BFR50 -2.8 ± 0.8%). It may be speculated that BFR applied during cycling exercise in the heavy intensity domain shifted the working muscles to an O <sub>2</sub> dependent situation. The acceleration of the extraction kinetics could have reached a plateau, hence not permitting compensation for the slowdown of the blood flow kinetics, and slowing kinetics

Muscle Deoxygenation Rates and Reoxygenation Modeling During a Sprint Interval Training Exercise Performed Under Different Hypoxic Conditions.

This study compared the kinetics of muscle deoxygenation and reoxygenation during a sprint interval protocol performed under four modalities: blood flow restriction at 60% of the resting femoral artery occlusive pressure (BFR), gravity-induced BFR (G-BFR), simulated hypoxia (FiO <sub>2</sub> ≈13%, HYP) and normoxia (NOR). Thirteen healthy men performed each session composed of five all-out 30-s efforts interspaced with 4 min of passive recovery. Total work during the exercises was 17 ± 3.4, 15.8 ± 2.9, 16.7 ± 3.4, and 18.0 ± 3.0 kJ for BFR, G-BFR, HYP and NOR, respectively. Muscle oxygenation was continuously measured with near-infrared spectroscopy. Tissue saturation index (TSI) was modelled with a linear function at the beginning of the sprint and reoxygenation during recovery with an exponential function. Results showed that both models were adjusted to the TSI (R <sup>2</sup> = 0.98 and 0.95, respectively). Greater deoxygenation rates were observed in NOR compared to BFR (p = 0.028). No difference was found between the conditions for the deoxygenation rates relative to sprint total work (p > 0.05). Concerning reoxygenation, the amplitude of the exponential was not different among conditions (p > 0.05). The time delay of reoxygenation was longer in BFR compared to the other conditions (p < 0.05). A longer time constant was found for G-BFR compared to the other conditions (p < 0.05), and mean response time was longer for BFR and G-BFR. Finally, sprint performance was correlated with faster reoxygenation. Hence, deoxygenation rates were not different between the conditions when expressed relatively to total sprint work. Furthermore, BFR conditions impair reoxygenation: BFR delays and G-BFR slows down reoxygenation

Comment on: "How Biomechanical Improvements in Running Economy Could Break the 2-Hour Marathon Barrier".

Comment on: "How Biomechanical Improvements in Running Economy Could Break the 2-Hour Marathon Barrier'

DNA methylation changes during a sprint interval exercise performed under normobaric hypoxia or with blood flow restriction: A pilot study in men.

This crossover study evaluated DNA methylation changes in human salivary samples following single sprint interval training sessions performed in hypoxia, with blood flow restriction (BFR), or with gravity-induced BFR. Global DNA methylation levels were evaluated with an enzyme-linked immunosorbent assay. Methylation-sensitive restriction enzymes were used to determine the percentage methylation in a part of the promoter of the gene-inducible nitric oxide synthase (p-iNOS), as well as an enhancer (e-iNOS). Global methylation increased after exercise (p < 0.001; dz = 0.50). A tendency was observed for exercise × condition interaction (p = 0.070). Post hoc analyses revealed a significant increase in global methylation between pre- (7.2 ± 2.6%) and postexercise (10.7 ± 2.1%) with BFR (p = 0.025; dz = 0.69). Methylation of p-iNOS was unchanged (p > 0.05). Conversely, the methylation of e-iNOS increased from 0.6 ± 0.4% to 0.9 ± 0.8% after exercise (p = 0.025; dz = 0.41), independently of the condition (p > 0.05). Global methylation correlated with muscle oxygenation during exercise (r = 0.37, p = 0.042), while e-iNOS methylation showed an opposite association (r = -0.60, p = 0.025). Furthermore, p-iNOS methylation was linked to heart rate (r = 0.49, p = 0.028). Hence, a single sprint interval training increases global methylation in saliva, and adding BFR tends to increase it further. Lower muscle oxygenation is associated with augmented e-iNOS methylation. Finally, increased cardiovascular strain results in increased p-iNOS methylation

Impact of systemic hypoxia and blood flow restriction on mechanical, cardiorespiratory, and neuromuscular responses to a multiple-set repeated sprint exercise.

Introduction: Repeated sprint cycling exercises (RSE) performed under systemic normobaric hypoxia (HYP) or with blood flow restriction (BFR) are of growing interest. To the best of our knowledge, there is no stringent consensus on the cardiorespiratory and neuromuscular responses between systemic HYP and BFR during RSE. Thus, this study assessed cardiorespiratory and neuromuscular responses to multiple sets of RSE under HYP or with BFR. Methods: According to a crossover design, fifteen men completed RSE (three sets of five 10-s sprints with 20 s of recovery) in normoxia (NOR), HYP, and with bilaterally-cuffed BFR at 45% of resting arterial occlusive pressure during sets in NOR. Power output, cardiorespiratory and neuromuscular responses were assessed. Results: Average peak and mean powers were lower in BFR (dz = 0.87 and dz = 1.23, respectively) and HYP (dz = 0.65 and dz = 1.21, respectively) compared to NOR (p < 0.001). The percentage decrement of power output was greater in BFR (dz = 0.94) and HYP (dz = 0.64) compared to NOR (p < 0.001), as well as in BFR compared to NOR (p = 0.037, dz = 0.30). The percentage decrease of maximal voluntary contraction of the knee extensors after the session was greater in BFR compared to NOR and HYP (p = 0.011, dz = 0.78 and p = 0.027, dz = 0.75, respectively). Accumulated ventilation during exercise was higher in HYP and lower in BFR (p = 0.002, dz = 0.51, and p < 0.001, dz = 0.71, respectively). Peak oxygen consumption was reduced in HYP (p < 0.001, dz = 1.47). Heart rate was lower in BFR during exercise and recovery (p < 0.001, dz = 0.82 and p = 0.012, dz = 0.43, respectively). Finally, aerobic contribution was reduced in HYP compared to NOR (p = 0.002, dz = 0.46) and BFR (p = 0.005, dz = 0.33). Discussion: Thus, this study indicates that power output during RSE is impaired in HYP and BFR and that BFR amplifies neuromuscular fatigue. In contrast, HYP did not impair neuromuscular function but enhanced the ventilatory response along with reduced oxygen consumption