Eccentric training combined to neuromuscular electrical stimulation is not superior to eccentric training alone for quadriceps strengthening in healthy subjects: a randomized controlled trial.

Background: Both eccentric training and neuromuscular electrical stimulation (NMES) are used for quadriceps strengthening. However, the effects of these interventions combined are unclear.

Objectives: To compare the effects of eccentric training combined to NMES and eccentric training alone on structure, strength, and functional performance of knee extensor muscles of healthy subjects.

Methods: This is a three-arm, single-blinded, randomized controlled trial. Forty-three volunteers (18-35 years) completed the full study schedule: control group (n=15); eccentric training group (ECC; n=15); and eccentric training combined to NMES group (ECC+NMES; n=13). Eccentric training program was performed twice a week for 6 weeks. A biphasic pulsed current (400μs; 80Hz; maximal tolerated intensity) was applied simultaneously to voluntary exercise for ECC+NMES group. Muscle structure (ultrasonography of vastus lateralis - VL, and rectus femoris - RF), strength (isokinetic dynamometry) and functional capacity (single hop test) were assessed before and after the training program by blinded researchers to groups allocation.

Results: Control group had no changes throughout the study in any outcome. Eccentric training (with or without NMES) did not affect concentric peak torque, hop test, and VL pennation angle (effect sizes>0.2). ECC and ECC+NMES programs generated significant adaptations (small to moderate effect sizes) on isometric (8-11%) and eccentric (13%) peak torques, VL muscle thickness (5%), VL fascicle length (5-8%), RF muscle thickness (8-9%), RF pennation angle (-2%), and RF fascicle length (12%).

Conclusion: NMES combined to eccentric training did not influence consistently the type or magnitude of adaptations provoked by knee extensor eccentric training alone in healthy subjects.