Acute Effects of Low-Load Blood Flow Restriction Exercise on Vastus Lateralis Electromyographic Activity in Healthy Young Adults: A Pilot Randomized Study

Background: Low-load resistance exercise with blood flow restriction (BFR) may increase neuromuscular stimulation while reducing external load. This pilot study examined the acute effects of unilateral knee extension at 20% one-repetition maximum (1RM) with BFR at 80% estimated arterial occlusion pressure (AOP), compared with the same protocol without BFR, on vastus lateralis surface electromyographic (sEMG) activity in healthy young adults. Methods: Twenty participants were randomized to receive BFR on either the dominant (n = 10) or non-dominant limb (n = 10); the contralateral limb completed the non-BFR condition. Both conditions were performed in randomized order during one session, separated by 10 min. Each limb completed 75 repetitions (30-15-15-15) at 20% of its limb-specific 1RM. The prespecified primary outcome was normalized RMS amplitude across 12 protocol windows, analyzed using a linear mixed model. Results: Normalized RMS amplitude was higher under BFR (between-condition difference, 21.12%MVIC; 95% CI, 14.54 to 27.71; p < 0.001). Exploratory analyses showed higher global mean and peak RMS under BFR, whereas within-protocol RMS change and temporal slope did not differ. The post-exercise percentage reduction in MVIC-derived RMS amplitude was smaller under BFR (−0.6 ± 14.1% vs. −15.4 ± 12.3%; p = 0.002). Significant secondary findings remained significant after Holm adjustment. No adverse events were spontaneously reported or observed immediately. Conclusions: Under this acute laboratory protocol, individualized BFR was associated with higher vastus lateralis sEMG amplitude than unrestricted exercise. MVIC-derived findings were exploratory and should not be interpreted as evidence of preserved strength or reduced neuromuscular fatigue. Larger studies, including clinical populations, are required.