AUTHOR=Solsona Robert , Berthelot Hugues , Borrani Fabio , Sanchez Anthony M. J. 

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

JOURNAL=Frontiers in Physiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2021.773950

DOI=10.3389/fphys.2021.773950

ISSN=1664-042X

ABSTRACT=<p><bold>Objective:</bold> 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.</p><p><bold>Methods:</bold> 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.</p><p><bold>Results:</bold> Regarding mechanical responses, peak and average power decreased after each sprint (<italic>p</italic> &lt; 0.001) excepting between sprints four and five. Time to reach peak power increased between the three first sprints and sprint number five (<italic>p</italic> &lt; 0.001). RPE increased throughout the exercises (<italic>p</italic> &lt; 0.001). Of note, peak and average power, time to achieve peak power and RPE were lower in G-BFR (<italic>p</italic> &lt; 0.001). Results also showed that SpO<sub>2</sub> decreased in the last sprints for all the conditions and was lower for HYP (<italic>p</italic> &lt; 0.001). In addition, Δ[O<sub>2</sub>Hb] increased in the last two sprints (<italic>p</italic> &lt; 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 (<italic>p</italic> &lt; 0.001). Moreover, muscle blood concentration was higher for BFR<sub>60</sub> (<italic>p</italic> &lt; 0.001). Importantly, average and peak oxygen consumption and muscular oxyhemoglobin availability during sprints decreased for HYP (<italic>p</italic> &lt; 0.001). Finally, the tissue saturation index was lower in G-BFR.</p><p><bold>Conclusions:</bold> 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.</p>