Introduction

One advantage of flywheel resistance training (FRT) is the ability to provide eccentric loading at different loads and velocities across a wide array of movement patterns. For example, by adjusting the inertial load on the device, you can target anything from very fast to very heavy eccentric loads. This is combined with useful characteristics such as resistance that is dependent on the input from the user (“user-defined resistance”), which helps ensure a safe and effective training stimulus for a wide range of users. And this unique loading can be provided to a wide range of movement patterns that can often be tricky to load in the same way using traditional equipment and methods.

What is Eccentric Overload in Flywheel Training?

With standard FRT, the momentum you develop as you accelerate the flywheels concentrically provides the resistance eccentrically in an approximately 1:1 ratio. While this still provides an effective eccentric training stimulus compared to other methods, there are several ways we can amplify the eccentric loading to provide a unique challenge to eccentric force capabilities over time. Notably, these methods allow for “eccentric overload”, or eccentric outputs that exceed max concentric outputs for either part or the entire eccentric range of motion (ROM).

3 Methods to Amplify the Eccentric Stimulus

More specifically, in this blog, I want to summarize three commonly used methods that can be used to progress the eccentric training stimulus with FRT and some of the considerations with their use.  

1. Delayed Braking  

2. Assisted Concentrics

3. Exerfly Motorized Boost

1. Delayed Braking

Braking strategies used during the eccentric phase can influence the loading. After accelerating the flywheel, the rope will rewind in the opposite direction, and you then need to produce braking forces to decelerate the flywheel and transition into the next rep. If you use a standard braking strategy, you will attempt to decelerate the flywheels across the entire ROM.  

However, with a delayed braking strategy, you allow the flywheel’s momentum to pull you through the first part of the eccentric phase and then brake hard and fast towards the later portions of the phase. This does not change the total braking impulse (force x time) required, but it does distribute the braking demand to a narrower timeframe. This is meant to result in a sharper, taller force-time curve where the peak braking forces and power are higher than with a standard braking strategy.  

This strategy is the most common method in the research for attempting to achieve eccentric overload during FRT exercises (2).  

Check out a couple examples of this method with a bent over row and trunk rotational exercise. In each case, the goal was to brake hard and fast during later portions of the eccentric phase and quick re-accelerate into the next rep.  

A few things to consider with this strategy:

• The total eccentric loading is still dependent on the concentric input, but it is condensed to a brief timeframe of intense braking effort.  
• Delayed braking tends to have a greater technical and physical demand than standard braking strategies. We generally recommend that new FRT users gain competency and confidence with standard braking first, before progressing to delayed braking.  
• This method only challenges the portion of the eccentric ROM where the delayed braking occurs. Muscle activation and loading will be minimal during the early parts of the eccentric phase as a result (1).
• Delayed braking results in a large demand close to the eccentric-concentric transition point, which can be useful when developing the ability to rapidly change direction during different movement patterns. In fact, FRT with delayed braking can result in substantial stretch shortening cycle use, particularly when used with low-moderate inertial loads (4).  
• Because the exact technique used will vary rep to rep and set to set, it is challenging to standardize the amount of extra eccentric demand this provides. Though you can still quantify progress by monitoring eccentric outputs over time.  

2. Assisted Concentrics

While delayed braking simply re-distributes a given eccentric resistance to a specific portion of the range of motion, assisted concentric methods increase the total eccentric demand. Because the eccentric resistance is dependent on the momentum of the flywheels developed during the concentric phase, techniques that provide extra assistance concentrically will result in a higher-than-normal eccentric demand.  

This approach was recently found to be effective for increasing the eccentric outputs while maintaining similar levels of ratings of perceived exertion (3). There are a few techniques that I commonly use with upper body and trunk FRT exercises.  

The first involves assisting the concentric phase with extra leg contribution. By using more muscle mass during the concentric phase than the eccentric, you can better accelerate the flywheels, increasing the eccentric demand. The video below shows two variations during a trunk rotation exercise. The first involves additional concentric leg extension to help accelerate the flywheels. In the second, a lateral step is used to add extra momentum. In each case, the load is primarily decelerated with the trunk.

Another option is a bilateral assisted concentric or using both sides to accelerate the flywheels and just one side to decelerate. For example, the video below shows a bilateral concentric phase into a unilateral eccentric phase. This results in greater momentum to decelerate than could be achieved with a purely unilateral action.

A few things to consider about this method:  

• It can be a convenient way of increasing the eccentric demand to different movement patterns.  
• Unlike the delayed braking method, it can amplify the eccentric loading across the entire range of motion rather than just a condensed portion.  
• Like the delayed braking method, it can require some technical competency, and it can be hard to standardize exactly how much extra eccentric resistance is provided.  

Exerfly Motorized Boost Technology

A unique feature of Exerfly FRT devices is the option to add Motorized Boost Technology, which provides extra “eccentric boost” to the flywheels. In this way, you can add a precise amount of extra momentum to the flywheels at the end of the concentric phase, which can be prescribed and/or progressed in as little as 1% boost increments.  

This eccentric boost can be applied to any number of exercises and at different loads. For example, adding the extra boost to a lighter inertial load provides a fast eccentric training stimulus, while adding it to a high inertial load can provide a form of AEL due to the additional eccentric resistance provided.  

For more insights into different ways to use the eccentric boost, check out this previous blog.

Summary Table of Eccentric Loading Methods

The table below provides an overview of the different methods, how they can progress the eccentric resistance, and some key considerations.  

While most people will apply one of these methods it’s important to note that you can combine them as well. For example, you could use a motorized boost while also delaying braking strategy to target the eccentric-concentric transition point. However, this is likely reserved for advanced trainees and/or used conservatively at first given the technical and physical demands that it would provide.  

Progressing the Eccentric Demand

The methods described in this blog allow for “eccentric overload”, or eccentric outputs that exceed concentric outputs. This is a particularly useful aspect of FRT compared to traditional training methods.

But when do you progress to these methods?  

We generally recommend that new users spend a bit of time learning the basics of flywheel training with non-motorized FRT using standard braking strategies before intentionally trying to amplify the eccentric loading. Once they have built up confidence and technical competency with standard FRT strategies, then you can start to introduce amplified eccentric loading through one of the methods discussed in this blog to drive even greater gains!

Looking for advice on how to introduce FRT to new users? Check out this blog for a deep dive into the topic.  

References

1. Calatayud, J., Pérez‐Alenda, S., Carrasco, J. J., Cruz‐Montecinos, C., Andersen, L. L., Bonanad, S., ... & Casaña, J. (2021). Feasibility, safety and muscle activity during flywheel vs traditional strength training in adult patients with severe haemophilia. Haemophilia, 27(1), e102-e109.

2. Martínez-Hernández, D. (2024). Flywheel eccentric training: how to effectively generate eccentric overload. Strength & Conditioning Journal, 46(2), 234-250.

3. Wren, C., Beato, M., McErlain-Naylor, S. A., Iacono, A. D., & De Keijzer, K. L. (2023). Concentric phase assistance enhances eccentric peak power during flywheel squats: Intersession reliability and the linear relationship between concentric and eccentric phases. International Journal of Sports Physiology and Performance, 18(4), 428-434.

4. Martinez-Aranda, L. M., & Fernandez-Gonzalo, R. (2017). Effects of inertial setting on power, force, work, and eccentric overload during flywheel resistance exercise in women and men. The Journal of Strength & Conditioning Research, 31(6), 1653-1661.

‍