Resistance training using eccentric overload induces early adaptations in skeletal muscle size

Area of Science:

• Exercise Physiology
• Sports Science
• Biomechanical Engineering

Background:

• Resistance training is crucial for muscle hypertrophy and strength.
• Different training modalities, such as weight stack (WS) and flywheel (FW) devices, offer distinct resistance profiles.
• Flywheel devices enable eccentric overload, a potentially potent stimulus for muscle adaptation.

Purpose of the Study:

• To compare the effects of flywheel (FW) versus weight stack (WS) resistance training on knee extensor strength and quadriceps muscle hypertrophy.
• To investigate whether eccentric overload provided by FW training leads to superior muscular adaptations compared to WS training.

Main Methods:

• Fifteen healthy men underwent a 5-week training program (2-3 sessions/week) using either a WS machine or an FW device for unilateral knee extensions.
• Maximal isometric force (MVC) and quadriceps muscle volume (via MRI) were assessed pre- and post-training.
• Task-specific performance was measured using device-inherent features.

Main Results:

• Maximal isometric force (MVC) increased significantly across all angles with FW training, but less consistently with WS training.
• Quadriceps muscle volume increased in both groups, with a trend towards greater hypertrophy (6.2% vs. 3.0%) in the FW group.
• All four individual quadriceps muscles showed increased volume in the FW group, while only m. rectus femoris increased in the WS group.

Conclusions:

• Flywheel resistance exercise, characterized by eccentric overload, may provide a more robust stimulus for muscle hypertrophy and strength gains compared to weight stack training.
• Eccentric overload is a key factor in optimizing the benefits of resistance exercise for muscle adaptation.