Whole-repetition quadriceps sEMG during flywheel squat and leg press: a randomized crossover study

Purpose Flywheel squat and leg press differ simultaneously in resistance characteristics, body support, posture, movement-control demands, and loading strategy. This study compared the whole-repetition surface electromyographic (sEMG) amplitudes of the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) between the two exercise configurations. Methods Following two familiarization sessions, 18 resistance-trained men (age: 22.4 ± 3.6 years; body mass: 77.7 ± 11.2 kg; height: 181.1 ± 6.2 cm) completed both exercises in a randomized, counterbalanced crossover design, with 7 days between sessions. Each condition comprised three sets of six analyzed repetitions with 2-min recovery. Flywheel sets included two preparatory repetitions and were performed with individualized inertia and maximal concentric intent; leg press used participant-specific 6RM-based loading and a cadence prescribed from familiarization. Root mean square sEMG was normalized to maximum voluntary contraction and calculated across each complete repetition, combining concentric and eccentric phases. The primary outcome was the mean across 18 repetitions per condition. Muscle-specific linear mixed-effects models adjusted for sequence and period, with Benjamini–Hochberg correction across muscles. Results No significant between-exercise differences were detected after multiplicity adjustment. Flywheel-minus-leg-press differences were −9.90 percentage points for RF (95% CI [−20.81, 1.01], adjusted p = .192), 2.58 for VL (95% CI [−7.33, 12.49], adjusted p = .588), and 8.57 for VM (95% CI [−2.76, 19.89], adjusted p = .192). Point estimates favored the leg press for RF and the flywheel squat for VM, but all confidence intervals included zero. Set effects were detected for RF and VL, but absolute changes were approximately 0.5 percentage points, with no Exercise × Set interaction. The VM: VL ratio was inconclusive (ratio of ratios = 1.07, 95% CI [0.89, 1.29], p = .451). Conclusion The data did not establish a clear difference between flywheel squat and leg press in mean whole-repetition RF, VL, or VM sEMG amplitude. The confidence intervals, particularly for RF and VM, remained compatible with both no difference and potentially meaningful muscle-specific effects; equivalence was not tested.