‍Background and Purpose 

Flywheel training devices offer several unique characteristics, including the ability to apply high effort throughout the entire range of motion and eccentric overload. The purpose of this study was to compare flywheel vs traditional weight stack knee extensions on muscle activation and other neuromuscular outcomes.  

Methods 

17 healthy male individuals were randomly assigned to either perform leg extensions on a flywheel training device (FRT; n=9) or a traditional weight stack device (TRT; n=9). Both groups completed 12 sessions across 5 weeks, with each session involving four sets of 7 reps of unilateral leg extensions. The FRT group was asked to use maximal effort during the concentric phase and then a delayed braking action to target a brief period of eccentric overload. Measures of isometric muscle strength, rate of force development (RFD), and muscle activation with surface EMG were taken before and after the training intervention.  

Results 

The key finding from this study: 

•  The flywheel leg extension involved significantly greater muscle activation of the vastus lateralis and medialis, particularly during the eccentric phase of the movement.  

• There were also several differences in terms of the muscle activation patterns across the movements. The traditional weight stack leg extension involved high muscle activation near the “sticking point” of the movement towards the end of the concentric phase, but muscle activation dropped substantially during the eccentric phase. In contrast, the flywheel variation involved high muscle activation across much of both phases of the movement.  

• The flywheel group also had a larger average increase in max isometric strength compared to the traditional weight stack group (+8.1% vs 4.8%)  

Key Takeaways 

Because each individual muscle fiber can produce greater total force during eccentric actions than concentric actions, there tends to be a drop in total muscle activation during the eccentric phase of traditional resistance training exercises. This study highlights how flywheel training can maintain higher eccentric muscle activation due to the eccentric loading it offers.  

Flywheel training exercises also provide different muscle activation patterns during the concentric phase than traditional methods. For example, the highest effort during traditional resistance training exercises occurs at the “sticking point” of the movement. In contrast, flywheel exercises allow for high muscle effort across the entire range of motion.