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How Alex Natera & NSW Institute Of Sport Use The Exerfly

Alex Natera is a coach, Performance Science Manager, and Performance Consultant at Natera Performance Solutions. With over 20 years of experience as a fitness professional, Alex has been using flywheel training devices for over 15 years, mainly for lateral movements or during the registered testing pool (RTP) process.

As put by Alex, "Although you can do 'technical things' to get a true eccentric overload with flywheel devices, generally, "what you put in is what you get out." For such a strong muscle action, this has always been hard for me to comprehend."

Alex recently added the Motorised Portable Rack Mount to his arsenal of flywheel devices, which he describes as “A beauty, and really starts to get me excited that such a versatile piece of kit, of which flywheels are, can now provide serious overload to tap into eccentric strength capabilities and not just emphasise them.”

Flywheel Training

Flywheel Training uses inertial disks to generate resistance, unlike traditional training, which relies on pulling a weight against gravity to generate the same resistance level for each rep. With Exerfly, the user uses their force to accelerate and decelerate the flywheel.

Whatever force is put into the concentric phase will be returned in the eccentric phase, so the harder and faster the user pulls, the harder and faster the resistance, or vice versa. Rep-by-rep, resistance constantly adapts to the individual's effort, catering to increasing fatigue and allowing athletes to perform maximally at every rep.

Flywheel Training Devices

Flywheel training devices have been around for decades

  • Flywheel devices can be either a horizontal cylinder or a vertical cone.
  • The main difference between a horizontal cylinder (HC) device and a vertical cone (VC) device is the rotating shaft shape, while in the VC-shaped device, the shaft has a decreasing radius from the base to the top. In the HC-shaped device, the radius increases due to the strap winding around the rotating shaft.

With traditional flywheels, we can do some "tricks" to get some more substantial eccentric "overload" - like assisting the concentric portion, braking over shorter distances, or braking at weaker muscle lengths.

There is no need for tricks with Exefly’s motorised technology:

  1. Just set the length and calibrate.
  2. Set your "Boost %" to amplify the energy of the flywheel up to a massive 80% of overload with no "tricks" needed.
  3. Enable the motor, start the windup, sit back, and let the unit do its thing.
  4. Hit the reps, get instant feedback and receive the true motor-powered eccentric overload.
  5. Enjoy every metric you could possibly want at your fingertips.

Eccentric training has always been a huge part of Alex’s training philosophy, having used flywheel/isoinertial devices for over 15 years. In particular, Alex has tended to use flywheels for lateral movements and in RTP. “Accentuated and augmented eccentrics methods have always been my preferred eccentric training method. I'm excited to dive into this motorised technology that's alway been a gap for me with flywheel training.”

Motorised Technology

Exerfly's innovative electric motor technology provides more energy to the flywheel in the eccentric phase of a movement based on how much energy the user produces in the concentric phase rep-by-rep.

For example, if the Eccentric Overload Boost is set to 10%, you will give the flywheel 10% more energy in the eccentric phase of a movement than it had in the concentric phase. This makes the flywheel spin faster, making the user receive an increased eccentric overload, which is later reflected in the statistics of the Exerfly app.

Exerfly's Motorized Technology allows users to add an eccentric overload of up to 80%, based on the force put into the concentric phase. Overloading eccentrically can be highly beneficial in many different areas, including muscle hypertrophy and injury prevention.


Flywheel devices provide a gravity-independent stimulus that causes greater muscle activation and allows for brief episodes of eccentric overload.

A study on the effects after 6 weeks (15 sessions) of flywheel resistance training with eccentric overload on different functional and anatomical variables in professional handball players found a significantly better improvement in muscle power at different submaximal loads (PO), vertical jump height (CMJ and SJ), 20 m sprint time (20 m), T-test time (T-test), and Vastus-Lateralis muscle (VL) thickness compared a group that performed the same number of training sessions, including 4 sets of 7 maximum repetitions using a weight-stack leg-press machine.

Additionally, athletes from the eccentric overload resistance training group showed significant improvements concerning all the variables measured:

The results measured included maximal dynamic strength (1RM),

  • 1RM (ES = 0.72)
  • PO (ES = 0.42 - 0.83)
  • CMJ (ES = 0.61)
  • SJ (ES = 0.54)
  • 20 m (ES = 1.45)
  • T-test (ES = 1.44)
  • VL (ES = 0.63 - 1.64)

Many sports require repeated short, explosive efforts such as accelerations and decelerations during sprints with changes of direction. This study suggests that flywheel resistance training with eccentric overload affects functional and anatomical changes in a way that improves performance in well-trained professional athletes.

**Please note that Alex Natera has no partnership with Exerfly or financial gain from his posts.

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