(1) Background: Near-infrared spectroscopy (NIRS) is an innovative and non-invasive technology used to investigate muscular oxygenation. The aim of this study is to assess the within- and between-session reliability of the NIRS Portamon (Artinis, Elst, Netherlands) device following three sets of induced muscle ischemia. (2) Methods: Depending on the experimental group (G1, G2 or G3), a cuff was inflated three times on the left upper arm to 50 mmHg (G1), systolic blood pressure (SBP) + 50 mmHg (G2) or 250 mmHg (G3). Maximum, minimum and reoxygenation rate values were assessed after each occlusion phase, using a Portamon device placed on the left brachioradialis. Reliability was assessed with intraclass correlation coefficient (ICC) value and ICC 95% confidence interval (CI-95%), coefficient of variation (CV) and standard error of measurement (SEM) (3) Results: Our results showed a good to excellent reliability for maximums and minimums within-session. However, the reoxygenation rate within sessions as well as measurements between sessions cannot predominantly show good reliability. (4) Conclusions: Multiple measurements of maximums and minimums within a single session appeared to be reliable which shows that only one measurement is necessary to assess these parameters. However, it is necessary to be cautious with a comparison of maximum, minimum and reoxygenation rate values between sessions.

Ischemic Preconditioning (IPC) has emerged as a promising approach to mitigate the impact of hypoxia on physiological functions. However, the heterogeneity of occlusion pressures for inducing arterial occlusion has led to inconsistent hemodynamic outcomes across studies. This study aims to evaluate the peripheral hemodynamic responses to partial and total blood-flow occlusions on the left arm at rest, using absolute or individualized pressures, on two occasions. Thirty-five young males volunteered to participate in this study. IPC procedure (3 × 7-min) was performed on the left upper arm with cuff pressures at 50 mmHg (G1), 50 mmHg over the systolic blood pressure (SBP + 50 mmHg) (G2) or 250 mmHg (G3). NIRS-derived parameters were assessed for each occlusion and reperfusion phase in the brachioradialis. Results showed a significantly lower magnitude of deoxygenation (TSIAUC) for G1 compared to G2 (−1959.2 ± 1417.4 vs. −10908.1 ± 1607.5, P < 0.001) and G3 -1959.2 ± 1417.4 vs. −11079.3 ± 1828.1, P < 0.001), without differences between G2 and G3. However, G3 showed a significantly faster reoxygenation only for tissue saturation index (TSI_slope) compared to G2 (1.3 ± 0.1 vs. 1.0 ± 0.2, P = 0.010), but without differences in the speed of recovery of deoxyhemoglobin [(HHb) slope], or in the magnitude of post-occlusive hyperemia (PORH). Besides TSI reoxygenation speed, G2 and G3 elicit comparable resting hemodynamic responses measured by NIRS. Thus, this study highlights the practicality and effectiveness of using relative occlusion pressures based on systolic blood pressure (SBP) rather than relying on excessively high absolute pressures.

Réponses et adaptations hémodynamiques et cardio-respiratoires à différents niveaux de restriction du flux sanguin, au repos et à l'exercice: L'ischémie induite par un brassard gonflé au repos (Ischemic Preconditioning, IPC) ou à l'effort (Blood Flow Restriction, BFR) affecte les paramètres de la chaîne de transport de l'oxygène, en fonction de la pression appliquée. Cette hypoxie locale est utilisée pour optimiser les effets de l'entraînement. L'objectif de ce travail de thèse est donc d'étudier les réponses et adaptations hémodynamiques et cardio- respiratoires à différents niveaux de restriction du flux sanguin, au repos ou à l'effort. Afin d'étudier les réponses hémodynamiques au repos, la fiabilité des mesures d'oxygénation musculaire obtenues avec de la spectroscopie infrarouge (NIRS) est testée. Les études menées dans ce travail doctoral montrent une excellente fiabilité des mesures intra-session, mais un manque de fiabilité inter-sessions. Au repos, l'oxygénation musculaire est affectée différemment entre une occlusion vasculaire partielle ou complète. Cependant, la réponse n'est pas différente entre une pression suprasystolique absolue et individualisée. A l'effort, quatre semaines d'entraînement aérobie à haute intensité couplé à différents niveaux de BFR améliorent la performance lors de l'épreuve maximale incrémentée et l'efficience à intensité sous-maximale, sans distinction entre les pressions d'occlusion. Ces résultats ouvrent des perspectives de recherche sur les processus physiologiques impliqués dans les réponses à l'hypoxie locale et suggèrent des applications du BFR dans l'entraînement aérobie pour améliorer les paramètres cardiovasculaires et respiratoires.