Standard V̇o₂ measures underestimate metabolic demand during blood flow-restricted exercise

Systemic oxygen consumption (V̇o₂) 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), V̇o₂ 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 postexercise oxygen consumption (EPOC). In a randomized crossover design, 18 recreationally active participants completed three, 3-min treadmill walking bouts, each separated by a 1-min 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 min of seated recovery. Expired gasses were recorded continuously. Walking Vo₂ was initially lower in the BFR condition compared with control (CON) (P = 0.0002), but reversed over time, with BFR producing a greater total walking Vo₂ (BFR: 16,638 ± 2,157 mL; CON: 15,219 ± 2,444 mL; P = 0.0006) and higher EPOC (BFR: 7,789 ± 837 mL; CON: 6,267 ± 1,102 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 V̇o₂. This suggests that acute, rate-based V̇o₂ 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.NEW & NOTEWORTHY This study challenges the reliability of V̇o₂ as a standalone marker of metabolic demand during blood flow-restricted (BFR) exercise. Although V̇o₂ during BFR walking was initially lower, a delayed rise during and prolonged recovery following BFR resulted in a greater total oxygen cost and excess postexercise oxygen consumption (EPOC). We suggest a temporal shift of oxygen dynamics, reflecting altered timing of uptake and recovery. Total oxygen uptake should be considered with BFR exercise.