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 post hoc comparisons, and effect sizes were reported. RPE was recorded immediately after the standardized isokinetic testing protocol (not during the jump tests). 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.