Do you know your eccentric overload?

Boosting Your Knowledge About Exerfly's Eccentric Boost Technology


One of the proposed benefits of flywheel resistance training (FRT) is its ability to achieve accentuated eccentric loading (AEL)  (3).  AEL is achieved when the eccentric mechanical output is higher in comparison to the concentric mechanical output (ie., power, velocity, force)  (4).  However, FRT typically provides a 1:1 ratio (concentric: eccentric), meaning that the energy applied in the concentric phase will be returned equally in the eccentric phase of the exercise.  Thus, AEL is not typically achieved with normal movement patterns on flywheels (5).  There are, however, a few strategies that may be performed to achieve AEL such as external assistance (i.e., T-bar assisted squats) or altered movement strategies (i.e., delayed or early breaking of downward momentum).  These strategies may pose challenges in the fields of exercise selection, program progression and the reliability of variables if external assistance is being used.

To date, the majority of the FRT research and practical application has focused on non-motorized technology.  Exerfly’s motorized technology allows you to boost the eccentric phase by 1 - 80% greater than the preceding concentric contraction.  The boost allows you to easily incorporate AEL across a wide range of exercises, ranges of motion and progress exercise intensity or load.  This is why high-level coaches have started to turn to Exerfly’s motorized technology.  However, motorized technology and its incorporation with flywheels is a relatively new innovation and there is limited information explaining how it can be used in a practical setting.   This blog aims to provide you with details on the different types of boosts, the benefits, and considerations that should be taken prior to implementing them.

Four types of boost:

  1. Wind-up boost
  2. Moderate AEL boost
  3. High force AEL boost
  4. High speed AEL boost

Wind-up boost can be implemented with < 5% boost with moderate to heavy load (.05 - .15 kg m2).  The primary purpose of this boost is not to achieve AEL.  Rather it is primarily used for the wind-up function.  By activating the wind-up, this initiates an 8 second countdown beep, then automatically pulls your athlete into their eccentric phase to start the exercise.  Without the wind-up, your athlete or another individual must spin the wheel for the exercise to start.  This is typically associated with a few warmup reps and occasionally some awkward starting positions.  The windup allows you to skip this phase, in which your athlete can start the movement directly after the windup is complete.

Moderate AEL boost can be implemented with 10 - 15% boost with heavy load (≥ .10 kg m2).  Maroto-Izquierdo et al. (2), investigated the training effects of moderate AEL and high force AEL across 10 weeks in 27 active university students.  The moderate AEL group increased their: maximal voluntary isometric contraction, muscular endurance, muscular power and favorable changes in hormones.  Although these researchers utilized an electric-motor device rather than a flywheel, the authors noted that similar adaptations could potentially occur with non-motorized flywheel devices if AEL was achieved due to the similarities that both devices share in respects to their kinematics and kinetics.  Moreover, Exerfly’s motorized technology is even more likely to share these similarities.  This moderate AEL boost is the first true boost on the flywheel that can be implemented with your athletes.  This also can be done with heavier inertial loads.  The heavier loads spin slower, which allows your athlete to get comfortable with utilizing the boost at slower movement speeds as well as gain the benefits of the boost.

High force AEL boost can be implemented with higher boosts (20 – 30%) with extremely heavy loading (≥ .20 kg m2).   As shown in the aforementioned investigation, high force AEL can have similar benefits as moderate AEL, however it likely can lead to greater improvements in 1 RM strength and jumping ability (2).  To achieve high force AEL greater inertial loads must be utilized to produce high forces.  In general, absolute strength work occurs around a concentric velocity of about .50 m/s (5).  Therefore, I recommend utilizing a load that would yield a similar velocity.  If the concentric velocity is < .50 m/s, a boost closer to 20% may be more appropriate, whereas > .50 m/s a boost of 30% can be utilized.  In general, we typically do not commonly recommend exceeding a 30% boost, however, with highly skilled and trained athletes and correct periodization you can exceed this 30% recommendation (see post below).

Click the link to see how high force AEL can be implemented.

High speed AEL boost can be implemented with 10 – 20% boost with light to moderate loads (≤ .05 kg m2).  Maroto-Izquierdo et al. (1), investigated training effects across 6 weeks in 40 active university students.  The subjects were divided into 3 groups; 1:1 ratio training elicited by an electric-motor device (EM group), and high speed AEL groups that were elicited by either an electric-motor device or delayed breaking strategy on a flywheel (AEL-EM and AEL-FRT groups, respectively).  All 3 groups increased muscle mass, vertical jump, muscular power, and 1RM.  The only difference found between the groups was that AEL-EM showed greater improvements in eccentric peak power during training in comparison to the AEL-FRT and EM groups.  It is important to note that the electric-motor device was not a flywheel, rather the machine was configured to provide a similar resistance that one would achieve with FRT.  Nevertheless, it seems that high speed AEL over the entire range of motion may lead to similar or greater improvements across performance assessments compared to 1:1 ratio training and delayed breaking FRT. Considering the velocity of movement in the concentric phase can be quite high, we recommend boosting the eccentric portion to 10 – 20%.  In addition, due to the extremely high movement speeds the considerations prior to implementing are the same as high force AEL boost (see considerations below).

Click the link to see how high speed AEL boost can be implemented.


A few factors such as technique, flywheel experience, and training age should be considered prior to implementing any boost.  It is important to note that these considerations are general guidelines for all populations.  If your athlete is able to execute non-motorized and motorized flywheel movement with proficient technique and is responding well to the dose, then the motor can be progressed in a linear nature regardless of flywheel experience and training age.  In addition, flywheel experience and training age are dependent variables, meaning that athletes with higher training ages could implement the boost with less flywheel experience and vice versa.  Lastly, your athletes/client’s skill level (i.e., middle school, D1, general population) and type of training environment (i.e., 1 on 1, small group, or team settings) will all influence some of the timelines listed below.  For instance, you may be able to implement the moderate AEL boost with a D1 athlete with an advance training age in a 1 on 1 environment as soon as their 3rd training session.   Whereas if you are working with middle school athletes with a lower training age in a team setting, they may need 1.5 months or greater before they are able to handle moderate AEL boost.

Wind-up boost considerations:

  • Flywheel technique: Your athlete must display proficient technique with non-motorized flywheel movements.  Some technique error may include: the inability to absorb the eccentric forces (“bottoming out”), a rigid transition from concentric to eccentric, or knee valgus.
  • Flywheel experience: You can implement the wind-up boost as soon as your athlete’s 3rd or 4th training session considering the marginal boost that is applied.

Moderate AEL boost considerations:

  • Flywheel technique: Your athlete should display proficient technique with flywheel movements.
  • Flywheel experience: Your athlete should have 1 – 1.5 months of FRT experience.
  • Training age: It is recommended that your athlete should have an intermediate training age (1 - 2 yrs).

High force and speed AEL considerations:

  • Flywheel technique: Your athlete must display proficient technique with motor and non-motorized flywheel movements.
  • Flywheel experience: Your athlete should have experience with motor and non-motorized flywheel training (≥ 2 months).
  • Training age: Your athlete should be intermediately to highly trained (2 - 3 yrs) and have strong relative strength in the respective exercise (both concentrically and eccentrically).


The 4 types of boosts that we commonly see implemented are the following: Wind up, moderate AEL, high force AEL, and high speed AEL boost.  You can program each boost for slightly different reasons and they will yield different training responses.  In addition, considerations such as flywheel experience, technique and training age should all be examined prior to you implementing each boost.  All 4 boosts are also listed in a somewhat progressive nature.  For instance, your athletes should become proficient with training with the wind-up boost, then move to moderate AEL boost, then finally high-force or high-speed AEL.


  1. Maroto‐Izquierdo, S, Fernandez‐Gonzalo, R, Magdi, HR, et al. Comparison of the musculoskeletal effects of different iso‐inertial resistance training modalities: Flywheel vs. electric‐motor. EJSS 19: 1184–1194, 2019.
  2. Maroto-Izquierdo, S, Martín-Rivera, F, Nosaka, K, et al. Effects of submaximal and supramaximal accentuated eccentric loading on mass and function. Front Physiol 14: 1176835, 2023.
  3. Muñoz-López, A, De Souza Fonseca, F, Ramírez-Campillo, R, et al. The use of real-time monitoring during flywheel resistance training programmes: how can we measure eccentric overload? A systematic review and meta-analysis. Biol Sport 38: 639–652, 2021.
  4. Muñoz-López, A, Nakamura, FY, and Beato, M. Eccentric overload differences between loads and training variables on flywheel training. Biol Sport 40: 1151–1158, 2023.
  5. Sánchez-Medina, L, Pallarés, J, Pérez, C, Morán-Navarro, R, and González-Badillo, J. Estimation of Relative Load From Bar Velocity in the Full Back Squat Exercise. Sports Med Int Open 01: E80–E88, 2017.

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The Exerfly Platform is a stable, multi-use flywheel training platform built for everything from heavy duty workouts to rehabilitation.

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