What do “Concentric phase” and “Eccentric phase” mean?
The concentric phase occurs when a muscle shortens or contracts, while the eccentric phase happens when a muscle lengthens or extends. With traditional weightlifting, most of the focus is on concentric loading, and the eccentric phase can be difficult to load manually. Flywheel training addresses this often-overlooked component, enabling you to strengthen your muscles in both directions with a single repetition.

By adding the Eccentric phase to your workouts, you can increase muscle strength more effectively than concentric exercises. This is because when muscles lengthen, fibers in the muscle split more than they do during concentric exercise. As more fibers split, the body works to rebuild them,
resulting in bigger muscles.

Due to the continuous nature of the resistance, flywheel machines are excellent for developing explosive power. The quick, reactive nature of the flywheel’s resistance encourages fast-twitch muscle fiber recruitment, which can be beneficial for athletes focused on speed, agility, and power development.

Because flywheel machines offer a continuous, variable resistance, they can improve muscular endurance by keeping muscles under constant tension for longer periods. This is especially beneficial for sports or activities that require prolonged exertion, such as long-distance running, cycling, swimming, or tennis.

Flywheel training helps muscles learn to maintain force over time, which can boost muscular stamina and fatigue resistance, allowing you to perform at a higher level for extended periods.

The variable resistance of flywheel training more closely mirrors real-life movement patterns than traditional gym machines or free weights. It requires you to engage stabilizer muscles and perform functional movements (e.g., pulling, pushing, rotating) in a more natural, multidirectional way.

This means flywheel training can improve your overall movement efficiency, coordination, and agility. It's particularly beneficial for athletes who need to move quickly and decisively in different directions, like in basketball, football, or soccer.

Flywheel training is joint-friendly and has been shown to help with injury prevention. The eccentric component of flywheel resistance promotes the development of tendons and ligaments, making them stronger and more resilient. This can reduce the risk of common injuries, particularly in high-impact sports.

Additionally, the gradual increase in resistance provided by the flywheel allows for safer progression compared to traditional weight training, where the load may increase too abruptly.

Because flywheel training engages muscles in various planes of motion, it can help improve joint mobility and muscle flexibility. Movements like rotational pulls or lateral pushes force the body to move in different directions, helping to develop greater range of motion and reducing the stiffness that can come from more linear forms of training (e.g., traditional weightlifting or running).

For athletes, increased mobility and flexibility are crucial for performing a wider variety of movements and for reducing injury risk, particularly in dynamic sports.

• Flywheel machines:

Provide a more dynamic, smooth, and continuous resistance. The resistance increases as you move faster or apply more force, and it keeps building as the flywheel accelerates. This mimics more natural movement patterns compared to the sometimes jerky feel of traditional cable machines.

• Cable machines:

Offer a fixed resistance based on the weight stack or load you’re using, which can feel more rigid and less adaptable.

• Flywheel:

The continuous resistance from the flywheel means your muscles experience greater time under tension throughout the full movement, which can lead to enhanced muscle growth and strength development.

• Cable machines:

Typically offer resistance only during certain parts of the movement, reducing the overall time under tension.

• Flywheel machines:

The resistance tends to remain relatively consistent throughout the entire range of motion,this provides a more uniform challenge for your muscles, especially if you're training for muscle endurance or power.

• Cable Machines:

Resistance changes based on the angle of the cable or the position of the pulley and is not as uniform.

Flywheel resistance can be gentler on joints than traditional free weights or some cable machines. This is due to the inertia-driven resistance, which typically feels more natural and fluid, as opposed to the more abrupt jerking movement often seen in cable machines.

For individuals with joint issues or those in rehab, flywheel machines may offer a more joint-friendly training experience.

• Flywheel resistance:

Machines excel in eccentric training (the muscle-lengthening phase of movement). Because the flywheel continues to spin even after you stop pulling or pushing, it creates resistance on both the concentric (lifting) and eccentric (lowering) phases of the exercise.

• Cable machines:

The focus is generally on the concentric (lifting) phase of the exercise, with eccentric resistance being less pronounced.

• Flywheel machines:

Often require a more full-body engagement because the momentum generated by the flywheel requires you to stabilize and use your core more intensely throughout the movement.

• Cable machines:

Tend to isolate muscles more, especially when using single-cable movements or fixed positions.

Flywheel machines, don’t rely on gravity in the same way that traditional free weights or cable machines do, meaning you can perform resistance exercises in varied angles and positions. This makes flywheel machines especially beneficial for targeting muscle groups in ways that may be difficult to achieve with cable machines.

• Flywheel machines:

The faster you move the more resistance you get (due to the increased momentum of the flywheel), making it easier to adjust resistance based on speed and force during the workout. This allows for a more functional training approach, especially for sports performance or explosive strength.

• Cable machines:

Usually offer fixed resistance depending on the weight you load, which doesn’t change dynamically based on your speed or force applied.

Inertia is a linear mass attribute that describes how well an item opposes a change in movement. The moment of inertia of a disc along an axis perpendicular to it and passing through its centre equals ½ * M * R^2, where M is the mass of the disc and R is the radius of the disc.

To put it simply, the harder you pull the faster you accelerate the wheel, wheels with more inertia (larger diameter and or more mass) take more force from you to accelerate.

The Inertia of the flywheel is what creates the resistance against the user of the Quest line of products. Flywheels are completely interchangeable between product models. Flywheels are sold in a variety of sizes to accommodate different resistance ranges. Flywheels can be combined to allow more resistance options, or to increase resistance beyond the use of a singe XL wheel.

Use the top range force equivalence for each flywheel below as a reference when selecting flywheels.

XS (15 lbs), Inertia .0038 KG*m^2

S (30 lbs) , Inertia .0075 KG*m^2

M (60 lbs), Inertia .0149 KG*m^2

L (120 lbs), Inertia .0297 KG*m^2

XL (250 lbs), Inertia .0616 KG*m^2

Actual resistance is created by the user and will be variable based on the velocity of your movements. However these values can be used as a guide to help select the range of flywheels necessary for your strengthening goals. When adding multiple plates you can add the pounds equivalents together to get an idea of how much resistance will be needed to accelerate the stack at about 1.5 m/s.

Most Users will not need more that a XL and a L wheel, this combo is about 370 Lbs of resistance. Multiple XL wheels require a very large amount of force to accelerate at a normal movement speed.

A Systematic Review of Flywheel Training Effectiveness and Application on Sport-Specific Performances

Authors: Juan M. García-Ramos, Francisco J. González-Badillo, et al.

Conclusion: Flywheel training is a safe and time-effective strategy to enhance physical outcomes, allowing for multidirectional replication and overloading of specific sports movements with a lower metabolic cost. In addition, it allows for optimal muscle strength production throughout the range of motion. Flywheel training can improve athletic performance in terms of strength, power, sprinting, jumping, and CoD. The literature suggests that at least two training sessions per week are needed to improve sport performance. However, information on quantifying volume, intensity, and load may be diversified to achieve training goals in different sports and at different technical levels in the future. It is advisable to include flywheel training in sport periodization in order to diversify the training stimuli for the athlete.

Link to Study

Effects of Flywheel Resistance Training on the Running Economy of Endurance Athletes

Authors: G. S. Hrysomallis, M. A. Sallis, et al.

Conclusion: Flywheel AEL training improved the lower limb explosive strength and jump performance including EUR, SJ, CMJ, and RFD of young male well-trained distance runners. Meanwhile, it also improved the athlete’s running economy under 65%, 75%, and 85% VO2peak, which potentially increased endurance performance. Moreover, the AEL training can be achieved by portable flywheel device whereas traditional high intensity strength training (e.g., Six RM) requires massive equipment including barbell, weight plates and rack. Apparently, flywheel AEL training with comparable exercise volume potentially provide superior training benefits to the traditional resistance training. Therefore, running or strength coaches and athletes who cannot access or carry strength training facilities should consider adding flywheel AEL training into their usual endurance for acquiring performance gain (American College of Sports Medicine, 2009).

Link to Study

Effects of Flywheel Training on Strength-Related Variables: a Meta-Analysis

Authors: Andrea M. Hwang, Henrik M. Skovgaard, et al.

Conclusion: Flywheel training is a strength training modality offering the possibility of performing exercises with eccentric overload and variable resistance that therefore differs from conventional gravity-based resistance training. Flywheel training seems to be a viable alternative to regular resistance exercise with comparable positive strength and hypertrophic adaptations in untrained, moderately trained, and well-trained individuals, with, surprisingly, greater strength improvements in the well-trained group and among younger individuals.In conclusion, flywheel training is an effective method for improving several aspects of strength and power with importance for sports performance

Link to Study

All Kratos Flywheel Machines are precision CNC-machined in the USA using high-quality materials. We provide a 2-year warranty on our machines and a 1-year warranty on the strap.

Our equipment has few wear components, but with enough use, parts like the strap and pulley sheaves may eventually need replacement. We stock replacement parts on our website and provide them free of charge within the warranty period. Bearings on most models are accessible and can be lubricated with Slick 50 or your preferred bearing lubricant as needed. These machines are mechanically sound and designed to last for many years.

We understand how important your fitness journey is, and we're here to support you every step of the way. When you reach out, we make it our priority to respond quickly—usually the same day, if not within hours. If any issues arise, we'll do whatever it takes to make things right. Your satisfaction is our commitment, and we’re always here to help you achieve your goals.

Returns and refunds are allowed up to 90 days after purchase if the product is used but determined to be defective, or if the product is still new but no longer wanted.