Effects of autoregulated and non-autoregulated blood flow restriction on vastus medialis oblique responses during low-load resistance exercise

Introduction/Purpose. Blood flow restriction (BFR) training is a viable strategy for inducing muscle hypertrophy and strength gains using low external loads. This study investigated the acute effects of autoregulated BFR (AR-BFR) and non-autoregulated BFR (NAR-BFR) using the Delfi Personalized Tourniquet System, and no BFR on vastus medialis obliquus (VMO) thickness, muscle oxygenation, hemoglobin concentration, and perceptual responses [rating of perceived exertion (RPE) and rating of perceived discomfort (RPD)].

Methods. Eighteen healthy adults (24.6 ± 2.3 years; 10 males, 8 females) performed a standardized single-leg wall squat protocol (1 × 30, 3 × 15 reps) under each condition in a randomized, crossover design.

Results. Both BFR conditions (AR-BFR and NAR-BFR) resulted in significantly greater increases in VMO thickness compared to the no BFR condition (p < 0.05), with no difference between the two BFR modalities (p > 0.05). Oxygen saturation significantly decreased across sets in both BFR conditions relative to no BFR (p < 0.05). However, AR-BFR initially maintained higher oxygen levels before declining to values comparable to those of NAR-BFR. Total hemoglobin levels were significantly elevated in both BFR conditions compared to no BFR (p < 0.05), with NAR-BFR producing the highest levels during the early sets. Both RPE and RPD were significantly greater in AR-BFR and NAR-BFR compared to no BFR (p < 0.05), with no significant differences between the two BFR protocols (p > 0.05).

Conclusion. These findings suggest that BFR training, regardless of autoregulated pressure application during exercise, produces acute physiological responses such as muscle swelling, localized hypoxia, and hemoconcentration that are conducive to initiating a stimulus that could elicit muscle hypertrophy in a training program. Although elevated perceptual demands accompanied these responses, the minimized mechanical joint stress supports the use of BFR as a clinically relevant alternative to high-load resistance training for individuals with limited tolerance to mechanical loading.