Exxentric Flywheel
With a higher inertia, the motion will be slower and more controlled. With a lower inertia, the motion will be faster which also puts higher demands on skill

starting from £ 85,19

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There are variations of this item. Please select the variation you wish.

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The kBox4 can be equipped with two or four flywheels simultaneously depending on the kBox model.

The flywheels are available in four different sizes:
  • Heaviest: 0.070 kgm2 (for kBox4 Pro only)
  • Heavy: 0.050 kgm2
  • Medium: 0.025 kgm2
  • Light: 0.010 kgm2

The average first-time user typically starts with one heavy flywheel for upper body exercises and two heavy for the lower body. The medium and light flywheels can be used both on their own for high-speed exercises and weaker individuals (such as for rehabilitation), but they can also be used to fine tune the inertia at higher loads.

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The Flywheel Workout Zones:
How to Pick the Right Inertia

Medium and High Speed Zones

Eccentric Training: The Force-Velocity RelationshipMoving on, increasing speed on a low inertia will put us first in more intense warm-up zone and also conditioning zone if we go for longer sets. Increasing speed further will put you in a power zone. Power output and speed is high, force is high but maybe not maximal in absolute values.

Inertia vs force

Generally inertia is low at the peak power. For the kBox Power Test, we see optimal range from 0.025 (some females) to 0.075 (male national level weightlifter) but the U-curve is much less pronouned on the kBox compared with weights. For finding a optimal inertia zone, plotting a power/inertia graph is recommended. Here is my power/inertia graph for the kBox Squat.


Working on strength and hypertrophy, you probably end up in the middle. From research in later years, we know low load training to momentary muscular failure can promote strength gains and mass as much as traditional loading but I think most people tend to do 5-12 reps if they are looking for strength and mass.

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Physical Principles

  • With flywheel training (also known as isoinertial or yoyo) instead of lifting a weight against gravity, you accelerate or decelerate a flywheel. This way, the force required in each motion is variable as it is based on the inertia and the kinetic energy of the flywheel. Read more.

Physiological Advantages

  • Flywheel training offers many advantages over traditional strength training. The resistance is variable and unlimited. Eccentric overload can easily be achieved as well as mobility, ergonomy and economy. Read more

Scientific Evidence

  • Multiple academic studies have provided support for flywheel training in recent years. We present a selection of some of the more important studies in the field. Read more.

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It could be a regular deadlift or stiff-legged deadlift. The experience of the eccentric phase in the #kBoxDeadlift will be new for most people. A nice exercise for lower back and hamstrings.

High pull
Can be a total body workout on the kBox thanks to the variable resistance and eccentric overload. Kick in with the legs and the eccentric phase will kick you back. Works deltoids, trapezius and arms in the regular setting and most of your upper body and core in the CLAC overload setting.

Biceps curl
With the Exxentric ultra light bar, this will be your new favorite exercise. Forget giving the biceps 12 sets in the gym. The kBox will do the work in 3 maximal sets with eccentric overload.

Triceps extension / over-head press
Slow and heavy with high force development with some core strength added. Perfect for a basic exercise to build strength and power in more complex exercises.

Bent-over row
After a couple of sets of rowing with eccentric overload you won't be able to go back to the traditional weights. It is a heavy exercise but still with a lot of power and motion, especially in the eccentric phase. It strengthens upper and lower back, shoulders and arms.


Datasheet K4Box_EN

K4Box User Manual_EN

K4Box User Manual_DE