Summary Points

• Flywheel testing allows you to quantify concentric and eccentric outputs during a wide range of sport or athlete relevant movement patterns.  

• Data collected from healthy athletes during routine flywheel testing sets can be used to benchmark typical performances and monitor responses to training.  

• After an injury occurs, an athlete’s individual benchmarking data can then be used as a reference point to guide and monitor the rehabilitation and return-to-play process post-injury.  

• In addition to testing use-cases, integrating flywheel sets into training and rehabilitation programs can also contribute to training benefits as well. For example, a few sets of high-intensity flywheel exercises at the start of a session can simultaneously offer 1) testing data, 2) a training stimulus, and 3) acute benefits on subsequent training exercises as a post-activation performance enhancement (PAPE) method.  

• This blog provides practical examples and recommendations for using flywheel testing efficiently for these purposes within athlete training and rehabilitation settings.  

Introduction

Flywheel training has several characteristics that make it a promising tool for injury prevention and rehabilitation settings. This includes isoinertial resistance, which provides high effort and muscle activation across the entire motion during each rep, and eccentric overload (3). This is supported by research which has successfully used flywheel training for hamstring injury prevention (2, 7), late-stage ACL rehabilitation (13,14, 22), patellar tendinopathy (1, 4), and in individuals with spinal cord injury (21).  

However, flywheel training devices can also contribute to injury prevention and rehabilitation processes as an assessment tool. Devices such as the Exerfly Ultimate and RackFly can measure mechanical outputs such as velocity, power, acceleration, and torque in real-time across a wide range of movement patterns.  

This is particularly useful for the purposes of measuring eccentric qualities, which is often constrained to simple isolated joint movements using tools like isokinetic dynamometers. Flywheel devices on the other hand can measure eccentric outputs across sport or injury-relevant movement patterns, while also doubling as an effective training methodology.  

Flywheels as a Sports Medicine Assessment Tool

Flywheel training devices such as the Exerfly Ultimate and RackFly can quantify a variety of mechanical outputs (e.g., velocity, torque, acceleration, etc.) across both the concentric and eccentric phases of a movement. When used effectively, this data can provide numerous benefits within sports medicine settings, such as the rehabilitation of patellar tendinopathy (PT) or other similar musculoskeletal concerns.  

PT is a common concern in jumping sports like volleyball and basketball and is often accompanied by neuromuscular changes such as reduced fascicle lengths and compromised eccentric strength and power (10,11,15). And a recent study found that elite athletes with PT demonstrated similar concentric outputs, but lower eccentric outputs during flywheel squat tests compared to their healthy counterparts (5). They suggested that such testing could be a useful way of assessing athletes with PT using sport-relevant movement patterns like the squat.  

Importantly, regular flywheel testing integrated into training and rehabilitation programs can allow for efficient data collection, which can then be used to benchmark and monitor healthy athletes, as well as to help guide the rehabilitation process. More to come on this concept below.  

Flywheel Testing Considerations

Effective flywheel testing requires a few considerations.

1. Familiarization: Athletes should be familiar with flywheel training, as it can often take multiple sessions for outputs to stabilize (16,20). Integrating regular flywheel testing into training can address this by providing consistent exposure to flywheel training, allowing for a reliable benchmarking dataset to be created over time.  

2. Technique Standardization: Technique can influence eccentric outputs during flywheel testing. For example, brief periods of eccentric overload can be obtained by using a delayed braking technique, where the athlete brakes hard and fast during the mid-late eccentric phase (3). Consistency in terms of instructions, cueing, and technical standards for the test exercise is important during both benchmarking and post-injury testing.  

3. Load Selection: Different flywheel inertial loads will result in different outputs. Lighter inertial loads result in faster movement velocities and quicker transitions, while higher inertial loads require greater mean force at slower velocities (17, 18). The loads selected during training should depend on whether you want to assess the athlete’s eccentric capabilities against a light/fast or heavy/slower eccentric load, or both. Additionally, you could perform baseline profiling methods to help select individualized loads (3). But if time is a constraint, then general standardized loads can be used to simplify the testing and training process. Regardless, it is important that load is standardized alongside technique to ensure a fair comparison over time.  

4. Statistical Analysis: How best to analyze results is an additional consideration. For example, when monitoring flywheel test results over time, you can create thresholds for a “meaningful change.” While there are multiple ways of doing this, one option is to quantify the variability of each measure during baseline sessions (e.g., standard deviation or coefficient of variation) and use that to set a threshold for what constitutes a meaningful change (12).  

Flywheel Test Example

With these considerations in mind, here is an example of how a flywheel test protocol could look.  

• Exercise: Half-Squat on the Exerfly Ultimate

• Technique Standardization: Maximal concentric effort through the entire range of motion. During the eccentric phase, gently resist for the first half of the motion, and then brake hard and fast during the second half.  

• Inertial Load: If time is limited, then an inertial load of 0.10 kgm² is a moderate load that tends to result in high power outputs for most athletes during Exerfly Ultimate half-squats. However, profiling methods can be used to individualize loads if time and resources allow for it (3).  

• Sets and Reps: 1-2 submaximal warm-up sets followed by 1 maximal effort set. Each set consists of 3 warm-up reps to build up momentum, followed by 8 maximal effort reps. Additional max effort sets can be added if time allows and if the goal is to simultaneously use testing as a training modality (see sections below).  

• Data Processing and Analysis: Velocity during concentric and eccentric phases is recorded during each rep of the max effort set. The average of the best 3 reps from the set is used as the measure of performance for that output. A moving average can be used to monitor progress and thresholds based on baseline standard deviation used to help detect meaningful changes.  

Now that we have an idea of what a flywheel test protocol could look like, let’s dive into how it can be used within a training and/or rehabilitation program.  

Practical Use-Cases of Flywheel Testing Within the Training Program

The study by Choi et al. (5) highlighted that flywheel squat eccentric outputs could be used to differentiate between athletes with and without PT. But how could this be incorporated into the practical setting? One approach is to 1) benchmark healthy athletes to develop individualized baseline outputs for key movement patterns, then 2) repeat testing to help guide the rehabilitation process. Notably, the assessment results could be calculated from standardized flywheel warm-ups or working sets which can serve multiple purposes simultaneously, including as a modality for post-activation performance enhancement (PAPE), training, and testing.  

Benchmarking

By adding standardized flywheel tests into the training routines of healthy athletes, you can establish individualized benchmarks for key outputs (e.g., eccentric velocity or power and ECC/CON ratios), while simultaneously using the flywheel sets as an effective warm-up and/or training exercise. This allows flywheel exercises to serve multiple purposes within a program in an efficient manner: 1) testing, 2) acute performance enhancement (i.e., PAPE), and 3) training stimulus.  

Below is a simple example of how this could work.  

In other words, the flywheel test protocol could be performed at the end of the warm-up or beginning of a training session, where it can contribute in 3 different ways simultaneously:

1. As a warm-up/PAPE, given that flywheel exercises can drive acute benefits in strength, power, and athletic performance measures (3).

2. As a training stimulus, since even low-volume flywheel exercises can drive neuromuscular adaptations over time and potentially reduce likelihood of injury or re-injury (2,3, 19)

3. As a testing method, by quantifying relevant mechanical outputs that can be used for benchmarking individual athletes over time.  

Over time, you can develop a benchmarking dataset, which is ready to be used in the unfortunate case of an athlete experiencing PT or another injury. Additionally, monitoring this dataset could be used as part of an athlete monitoring or “early detection” system, where unexpected drops in performance are explored further (see the figure below as an example). Additionally, progressive increases in outputs can be a positive sign that they are adapting to the training program in a positive manner.  

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Guiding and Monitoring Rehabilitation and Return to Play

In the case of an athlete experiencing PT (or another relevant musculoskeletal injury), flywheel testing can be used to compare outputs to the athlete’s individual benchmarking data to help guide and monitor the rehabilitation and return-to-play process.  

There are a few metrics that are worth monitoring.  

First, because the eccentric loading is dependent on concentric input against a given load, comparing concentric outputs to their healthy benchmarking values can be useful during rehabilitation. If someone is not confident in their ability to manage the eccentric load during max effort flywheel exercises, they will often ease back during the concentric phase to make the eccentric loading more manageable.  

Once they have re-established normal concentric outputs, then you can start to home in on measures like eccentric velocity or power. You’d ideally want to see an increase in these values back towards their benchmark testing as they progress back to healthy status.  

Finally, you can track these flywheel outputs alongside other neuromuscular testing and symptomology to get a more complete picture of their progression through rehabilitation or return-to-play. In this case, flywheel testing may be a useful way of identifying both the capacity and confidence to tolerate eccentric loading during dynamic, multi-joint tasks that are relevant to the athlete.  

Summary

Hopefully this blog gives you some thoughts on how flywheels could be used for testing purposes, in addition to training. Notably, the concepts discussed here could apply to a variety of other rehabilitation or clinical settings. For example, flywheel training has also been used successfully for a variety of rehabilitation and clinical purposes late-stage ACL rehabilitation (13,14, 22), and as a countermeasure against the negative neuromuscular effects experienced during aging (6) after experiencing a stroke (8,9), and after spinal cord injury (21). Additionally, flywheel testing could also be used for upper extremity injury situations as well. Therefore, this concept of integrating flywheel to both test and train could provide value across many different situations and circumstances.  

References

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2. Askling, C., Karlsson, J., & Thorstensson, A. (2003). Hamstring injury occurrence in elite soccer players after preseason strength training with eccentric overload. Scandinavian Journal of Medicine & Science in Sports, 13(4), 244-250.

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19. Petré, H., Wernstål, F., & Mattsson, C. M. (2018). Effects of flywheel training on strength-related variables: A meta-analysis. Sports Medicine-Open, 4, 1-15.

20. Sabido, R., Hernández-Davó, J. L., & Pereyra-Gerber, G. T. (2018). Influence of different inertial loads on basic training variables during the flywheel squat exercise. International Journal of Sports Physiology and Performance, 13(4), 482-489.

21. Santos, L. V., Freitas, K. R., Pereira, E. T., Leite, L. B., Forte, P., de Oliveira, C. E. P., & Moreira, O. C. (2025). Comparative Effects of Resistance Training Modalities on Mental Health and Quality of Life in Individuals with Spinal Cord Injury. Sports, 13(2), 60.

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