Reduced task-related quadriceps sEMG and limited functional transfer after 4-week low-load blood flow restriction training: a pilot randomized controlled study.

Background: Low-load blood-flow restriction training (BFR-LIR) can enhance strength-related adaptations with reduced mechanical stress, but whether it promotes task-related neuromuscular economy (lower task-related sEMG amplitude for comparable mechanical output) and how it compares with high-intensity resistance training (HIR) remains unclear. Objective: To compare the effects of 4 weeks of BFR-LIR, HIR, and LIR on isokinetic knee extensor performance, task-related neuromuscular activation, functional performance, and perceived exertion in healthy young men. Methods: Twenty-four healthy young men were randomized (1:1:1) to a low-load blood-flow restriction training group (BFR-LIR; ∼30% baseline isokinetic peak torque with individualized cuff pressure set at 70% arterial occlusion pressure [AOP] using a 10-cm pneumatic cuff), a high-intensity resistance training group (HIR; 8-12 RM), or a low-intensity resistance training group (LIR; ∼30% baseline isokinetic peak torque). All groups trained three times per week for 4 weeks. Outcomes were assessed pre- and post-intervention (isokinetic knee extensor peak torque at 60°/s and 120°/s, quadriceps sEMG during standardized isokinetic testing, countermovement jump and standing long jump performance, and ratings of perceived exertion). Between-group effects were evaluated using one-way ANOVA on Pre-Post change scores (Δ) with Holm-adjusted Results: Peak torque did not significantly change from pre-to post-intervention in any group at either velocity. Between-group comparisons of change scores (Δ) identified a significant group effect for Total Work at both 60°/s and 120°/s, driven by larger increases in HIR than LIR. Within-group Total Work increased at 60°/s in BFR-LIR and HIR, and at 120°/s in HIR. In BFR-LIR, Mean %MVC and dynamic RMS during isokinetic testing decreased at both velocities, whereas no consistent changes were observed in HIR or LIR. Hang time improved in HIR; standing long jump and RPE were unchanged across groups. No training-related adverse events were reported. Conclusion: Over 4 weeks, BFR-LIR was associated with small within-group improvements in isokinetic total work at 60°/s and reduced task-related quadriceps sEMG during isokinetic testing, whereas HIR showed the clearest improvement in hang time. Between-group differences in ΔsEMG were not significant, and changes did not translate to multi-joint jump performance over the short intervention period.