Get rid of your dumbbells and kettlebells, flywheel training is the next thing! Flywheel training (or inertia training) uses flywheel technology instead of weights. It is used by NASA in weightlessness space, where gravity – and therefore weight – does not work like us humans on earth would expect.
That is when the yo-yo effect of flywheel training comes in handy. Remember the yo-yo you used to play with as a child? It would start spinning as soon as the cord unwinds. When the cord is fully unwound, the yo-yo has a certain amount of kinetic energy. This will keep the yo-yo spinning in the same direction and will therefore wind the yo-yo up again. Because the energy of the unwind phase roughly equals the energy of the roll up phase, the yo-yo always came back to its upper starting position.
The yo-yo technology is not new. The first depiction of a boy playing with a yo-yo is to be found on an ancient Greek vase about 440 BC. Only recently this technology is implemented in fitness by Kynett among others. But why? On earth we do have gravity, so why would we use the NASA technology? I’ve been testing the Kynett ONE for a couple of weeks now and here I will share my thoughts about it.
1. Concentric and Eccentric muscle movements
First thing you notice: like with a classic yo-yo, the harder you pull, the harder the flywheel will spin and eventually pull back. The pull-phase feels vary natural because it is the same movement as when lifting a weight against gravity: you shorten your muscle like in a typical bicep curl. This movement is called concentric. But then, when the cord is fully unwound, the flywheel will start pulling back. You will need the same amount of energy to slow the flywheel down as you invested in the pull-phase. This movement, where your muscle lengthens, is called eccentric.
This I find a unique difference when comparing to regular weight training. In weight training you lift a weight against gravity, and gravity will help you to lower the weight. You only need a little eccentric energy to make sure the weight does not immediately fall on the ground. In other words, weight training does not focus on eccentric movements as much as flywheel training does.
Training the eccentric movement is proven to be more effective in increasing strength and muscle hypertrophy. A study in 2008 shows the effect of flywheel training being twice as big on muscle size growth than regular weight training. Read more about what eccentric training is (not) in another article I wrote.
2. Powerful muscles
Second thing you will notice is the focus on speed instead of (slow) strength. This will create more powerful muscles since power is a combination of strength multiplied by speed. In regular weight training it does not matter how fast you lift a weight. You could be able to lift a lot of kilograms, but be unable to do that with a certain amount of speed and therefore power. Although that might be cool at the gym, in most other situations that is useless. Think of a tennis player heaving strong arms, but no potential to create speed. Or a runner/cyclist with strong legs, but again not able to create speed in those legs. That is useless strength. Since flywheel training does focus on both speed and strength, I’m confident that this will better suit the needs of athletic performance and daily life.
Good to mention: that does not mean you can’t create strength with a Kynett. You can easily determine and vary your own intensity. I tested the standard Kynett disks, and found you can generate forces equal to a range of 0 to 100 kilograms. If that is not enough for you, you could simply buy thicker flywheel disks to increase the range.
3. Practical advantages
Last but definitely not least are the practical advantages I discovered. Because the Kynett is not based on weight training, it is lightweight and therefore easy to move. It truly fits into the trend of home fitness. During a rainy day, I use it indoor by fixing it to the Kynett wall bracket, stair railing or any other vertical pillar. When the sun is out, I prefer to use it outdoor by fixing it on a tree in a park or lamppost on the street. Since it takes up little space, I can’t wait taking it with me during holidays. Because you can easily adjust the intensity, you won’t need a full range of weights for yourself and your family.
Future talk
In the near future I expect innovations that will make a Kynett workout more measurable. For instance, by adding power and force measurements via an in between sensor like Powrlink. This is the sensor I used for measuring the force ranges mentioned earlier. You can then see your data live, optimize performance and compare it to your personal best.
I will definitely keep on testing and enjoying the Kynett ONE the upcoming weeks and send you an update later! For the meantime, you might want to discover flywheel training yourself :). 
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Founder of Molab, Human Movement Scientist and Freelance Content Marketer.