Near-Infrared Spectroscopy Assessment of Post-Occlusive Reactive Hyperemia and Muscle Metabolic Responses to Sustained Isometric Exercise Across Varying Anchor Scheme and Occlusion Conditions

This study examined post-occlusive reactive hyperemia (PORH) and muscle metabolic responses via near-infrared spectroscopy-vascular occlusion tests (NIRS-VOT) under four experimental conditions: (1) rating of perceived exertion (RPE)-Clamp, (2) blood flow restriction (BFR), (3) NON-BFR, each involving low-intensity, sustained isometric forearm flexion, and (4) PASSIVE BFR, a passive occlusion without exercise. Eighteen healthy young adults (11 males, 7 females) completed a sequence of pre-VOT, an experimental intervention, and post-VOT on separate days. During each intervention, time to task failure (TTF), percent changes in muscle oxygenation (SmO2 ), and performance fatigability (PF) were also assessed. RPE-Clamp exhibited a significant, positive change in SmO2 compared to negative changes in other conditions (p<0.003). PF did not differ between NON-BFR and BFR (p=1.000), but both were greater than RPE-Clamp and PASSIVE BFR, with RPE-Clamp greater than PASSIVE BFR (p=0.022). No differences were observed in TTF across conditions (p=0.455).Desaturation rate (oxygen extraction rate; slope 1) (p<0.001) and ischemic stimulus (MinSmO2 ) (p=0.001) were greater pre-than post-VOT. Reperfusion slope (slope 2) showed no significant differences by time (p=0.119) or condition (p=0.448). Peak SmO2 (MaxSmO2 ) was higher pre- than post-VOT (p=0.017), with NON-BFR (p<0.001) and BFR (p=0.005) greater than PASSIVE BFR. Area under the curve (AUC) above baseline SmO2 did not differ by time (p=0.695) but was greater in NON-BFR than PASSIVE BFR (p=0.010). Despite the distinct SmO2 responses and fatigue profiles across conditions, immediate post-intervention occlusion following prolonged isometric exercise or occlusion may have reduced oxygen extraction capacity and facilitated metaboreflex-induced sympathetic overactivity, collectively attenuating PORH.