Low‐ and high‐volume blood‐flow restriction treadmill walking both improve maximal aerobic capacity independently of blood volume

Aim Assess the effect of low‐ and high‐volume blood flow restriction training (BFR) on maximal aerobic capacity (VO 2 max) and determine if alteration in VO 2 max is mediated through changes in hemoglobin mass (Hbmass) and blood volume. Methods Participants' Hb mass (CO‐rebreathe), single, and double‐leg VO 2 max and blood volume regulating hormonal responses (renin and copeptin) were measured before and after BFR training. Training consisted of treadmill walking either (1) twice‐daily for 4week (CON and BFR HV ) or (2) twice‐weekly for 6week (BFR LV ). Each session consisted of five intervals (3 min, 5% incline, 5 km/h, 100% of lowest occlusion pressure), with 1 min of standing rest between sets. Results VO 2 max increased using both training exposures, in as quickly as 2‐weeks (BFR LV baseline to 4week: +315 ± 241 mL (8.7%), p = 0.02; BFR HV baseline to 2week: +360 ± 261 mL (7.9%), p < 0.01), for the BFR LV and BFR HV groups, with no change in CON. Single‐ and double‐leg VO 2 max improved proportionately (single/double‐leg VO 2 max ratio: BFR LV 78 ± 4.9–78 ± 5.8%, BFR HV 79 ± 6.5–77 ± 6.5%), suggesting that the mechanism for increased VO 2 max is not solely limited to central or peripheral adaptations. Hb mass remained unchanged across groups (CON: +10.2 ± 34 g, BFR LV : +6.6 ± 42 g, BFR HV : +3.2 ± 44 g; p = 0.9), despite a significant release of blood volume regulating hormones after initial BFR exposure (renin +20.8 ± 21.9 ng/L, p < 0.01; copeptin +22.0 ± 23.8 pmol/L, p < 0.01), which was blunted following BFR HV training (renin: +13.4 ± 12.4 ng/L, p = 0.09; copeptin: +1.9 ± 1.7 pmol/L, p = 0.98). Conclusion BFR treadmill walking increases VO 2 max irrespective of changes in Hb mass or blood volume despite a large release of blood volume regulating hormones in response to BFR treadmill walking.