Acute Central Stiffness and Muscle Morphological Responses Following Blood Flow Restricted Resistance Exercise with Autoregulated and Non-Autoregulated Pressure Application

Objective. To investigate the acute effects of autoregulated (AR) and non-autoregulated (NAR) blood flow restriction (BFR) resistance exercise to volitional fatigue on indices of arterial stiffness and muscle morphology using the Delfi Personalized Tourniquet System. Methods. Following a randomized AR-BFR/NAR-BFR familiarization session, 20 physically active adults (23±5 years; 7 female) participated in 3 randomized treatment-order sessions with AR-BFR, NAR-BFR, and No-BFR. Participants performed 4 sets of dumbbell wall squats to failure using 20% of 1 repetition maximum. BFR was performed with 60% of supine limb occlusion pressure. Testing before and immediately post-session included an ultrasonic scan of the carotid artery, applanation tonometry, and blood pressure acquisition. Vastus lateralis cross-sectional area (CSA), and echo intensity (EI) were also assessed via ultrasound before and after each session. Results. CF-PWV increased in the NAR-BFR and No-BFR groups following exercise while CR-PWV increased in the No-BFR group (all p < 0.05). CF-PWV exhibited an interaction effect between AR-BFR and NAR-BFR in favor of AR-BFR (p < 0.05). There were significant main effects of treatment for CSA (p=0.016) and EI (p=0.019) with all conditions on CSA and EI, with a greater increase in NAR-BFR. Conclusion. AR-BFR training does not influence indices of arterial stiffness while NAR-BFR and No-BFR training increases central stiffness. Additionally, low-load resistance exercise to failure induces muscle swelling regardless of BFR. However, NAR-BFR increased CSA and EI compared to AR-BFR. These findings suggest that AR-BFR causes a lower fluid flux to the intracellular space, possibly inducing less muscle damage and swelling than NAR-BFR.