Influence Of Blood Flow Occlusion On Muscle Oxygenation Profiles During Intermittent Maximal-effort Contractions

During intermittent, maximal-effort contractions (IMECs), limb blood flow occlusion has a profound and quickly reversible effect on motor unit excitation and fatigue development but its impact on microvascular oxygenation and intra-contraction oxygenation profiles remains unknown. PURPOSE: To test the hypothesis that limb blood flow occlusion would reduce contraction-to-relaxation differences (oscillations) in microvascular oxygenation during IMECs. METHODS: Sixteen participants (8 M/8F; 21 ± 2 yrs.) performed IMECs (forearm flexion) for 5-min under control conditions (CON) and with complete limb blood flow occlusion (OCC) followed by immediate reperfusion (REP). OCC was initiated at the start of the test and persisted until maximal-effort torque was <15% of initial maximal torque. REP was initiated immediately following OCC and IMECs were performed without interruption until the end of the 5-min test. Oxygenated- and deoxygenated-[heme] of the biceps brachii (oxy-[heme] and deoxy-[heme]) were measured by frequency-domain near-infrared spectroscopy. Total-[heme] and tissue saturation (StO2) were calculated. Data from 3 consecutive contractions were averaged at Start, Min-1, End-OCC (and time-matched CON), and End-test. RESULTS: Reductions in oxy-[heme] and StO2 were greater, and increases in total-[heme] were less, during OCC compared to CON (all, p < 0.05). No differences in deoxy-[heme] were detected between OCC and CON at any timepoint (End-OCC: 101 ± 60 vs. 109 ± 62 μM, p > 0.05). During CON, significant oscillations were detected for all signals (all, p < 0.05). OCC compressed oscillations in oxy-[heme] (Min-1: 22.7 ± 21.7 vs. 40.6 ± 31.3 μM, p < 0.01) and deoxy-[heme] (Min-1: 0.28 ± 7.75 vs. -7.87 ± 9.21 μM, p < 0.05) such that deoxy-[heme] remained high and oxy-[heme] remained low during relaxation. After REP, there were no differences in any oxygenation characteristics or oscillation sizes between CON and REP at End-test (all, p > 0.05). CONCLUSION: The unchanged deoxy-[heme] response with complete limb blood flow occlusion suggests no reserve exists for fractional oxygen extraction during IMECs. Like previous reports of motor unit excitation and fatigue, occlusion had a profound and quickly reversible effect on contraction-to-relaxation oscillations in microvascular oxygenation.