Physiological Responses to Intermittent Endurance Exercise with Blood Flow Restriction in the Moderate Intensity Domain

Abstract

Blood flow restriction (BFR) endurance training may induce both endurance and strength improvements. However, there is no consensus on the ideal BFR endurance exercise prescription in order to balance the physiological and perceptual responses. PURPOSE: The purpose of this investigation was to examine the physiological responses, as well as the perceived exertion in responses to a range of BFR endurance protocols. METHODS: Participants randomly performed 7 exercise protocols: 50% of the difference between peak oxygen uptake (VO2) and ventilatory threshold (VT) (∆50%), 90%, 80%, and 70% of VT with and without BFR. Each protocol consisted of two sets of five work intervals (2 minutes work, 1 minute rest) separated by 5 minutes of recovery. Pulmonary VO2 was recorded breath-by-breath, muscle activation (vastus medialis (VM), vastus lateralis (VL)) was assessed by surface electromyography (sEMG), microvascular oxygenation (tissue oxygenation index (TOI)) was assessed by near-infrared spectroscopy (NIRS), and level of perceived exertion (RPE) was assessed using the Borg scale. The last 30 seconds of intervals 5 and 10 were used for analysis. sEMG data were normalized to baseline cycling (20 watts). TOI during each condition was analyzed compared to baseline cycling and then expressed as change from baseline (arbitrary units) to compare between conditions. RESULTS: The ∆50% protocol resulted in a higher end exercise (interval 10) VO2 compared to all other conditions, no other differences in VO2 were observed. No sEMG differences were observed between conditions (VL- p = 0.24, VM- p = 0.33) or between interval 5 and 10. All BFR conditions resulted in a decrease in TOI from baseline. TOI was greater for all BFR conditions (70%BFR = -36.4 ± 21.9, 80%BFR = -40.4 ± 6.5, 90%BFR = -44.7±7.25) compared to the non-BFR conditions (70% = +4.3 ± 20.2, 80% = +11.8 ± 5.5, 90% = +7.25). No differences in TOI between ∆50 (-36.93 ± 10.8) and any BFR conditions were observed. RPE was greater during 90%BFR (18.0 ± 0) and 80%BFR (17.1 ± 1.1) compared to 70% (11.3 ± 0.6) and 90% (13.0 ± 0). No differences were observed between 70%BFR (14.6 ± 0.6) and non-BFR conditions. CONCLUSION: This study demonstrated that cycling with the addition of BFR at an intensity equivalent to 70% of VT may provide a balance between physiological strain and perceived exertion.