Standard ⩒O₂ Measures Underestimate Metabolic Demand during Blood Flow Restricted Exercise

Systemic oxygen consumption (⩒O₂) has traditionally been the gold standard for assessing aerobic metabolic demand. However, under conditions that alter normal blood flow or ventilation, such as blood flow restriction (BFR), ⩒O₂ may no longer reflect metabolic cost. The purpose of this study was to evaluate the total oxygen requirement (VO₂) of walking with and without BFR, including in-exercise VO₂ and excess post-exercise oxygen consumption (EPOC). In a randomized crossover design, 18 recreationally active participants completed three, three-minute treadmill walking bouts, each separated by a one-minute standing rest to simulate a typical repeated BFR protocol. In the BFR condition, tourniquets were applied to the upper thighs at 100% of the limb occlusion pressure throughout the interval protocol and removed for 15 minutes of seated recovery. Expired gasses were recorded continuously. Walking VO₂ was initially lower in the BFR condition compared to control (CON) ( p = 0.0002), but reversed over time, with BFR producing a greater total walking VO₂ (BFR: 16638 ± 2157 mL; CON: 15219 ± 2444 mL; p = 0.0006) and higher EPOC (BFR: 7789 ± 837 mL; CON: 6267 ± 1102 mL; p < 0.0001). The relative contribution of EPOC to total oxygen demand was elevated with BFR (BFR: 32.0 ± 2.8%; CON: 29.2 ± 2.1%; p = 0.0012), together indicating a time-dependent shift in ⩒O₂. This suggests that acute, rate-based ⩒O₂ does not fully capture the true metabolic demands of BFR exercise. Researchers should instead consider the total oxygen and recovery when interpreting metabolic load during BFR.