Inertia in Flywheel Training

Understanding the concept of inertia is key to reaping the benefits of flywheel training. Instead of using weights, the resistance in flywheel training is created through the inertia of a flyweel  which is rotated with muscle force.

Gravity vs Inertia

Traditional strength training is generally done by lifting some sort of weight – such as a barbell, dumbbell and weight stack machines – against gravity to create resistance.

In flywheel training or isoinertial training, resistance is created through the inertia of a flywheel, which is accelerated or decelerated with muscle force. The level of inertia of the flywheel rather than the weight determines the force needed. The principle is equivalent to that of a traditional yoyo device.

The resulting force in a flywheel training exercise depends on a combination of the inertia and the intensity you work with. With a higher inertia, the motion will be slower and more controlled, and your muscle will be able to produce a higher force. With a lower inertia, the motion will be faster which also puts higher demands on skill, balance and technique.

Inertia on the kBox and kPulley

The Exxentric flywheel training devices kBox and kPulley can be equipped with up to four flywheels with inertia ranging from 0.005 kgm² to 0.070 kgm². This facilitates an inertia range of 0.005 kgm² to 0.100 kgm² on the smallest model kBox4 Active, and up to 0.280 kgm² for the largest model kBox4 Pro.

  • Extra Large: 0.070 kgm²
  • Large: 0.050 kgm²
  • Medium: 0.025 kgm²
  • Small: 0.010 kgm²
  • Extra Small: 0.005 kgm²

Choosing Inertia

In flywheel training, choosing inertia means more than deciding between light and heavy. The inertia resulting from the size and number of flywheels impacts the training adaption you get.

Together with your workout intensity, the the ideal choice of inertia depends on your exercise purpose, also coined the Flywheel Workout Zones.

Learn more


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kBox4 Active

Our entry level model for the serious personal trainer or demanding home user. The perfect tool in strength and rehabilitation at our lowest price point.

  • Entry Level Model
  • Holds 1-2 Flywheels
  • kMeter Compatible
  • Weighs 15 kg
  • Starting at €1 410 / $1 635
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kBox4 Lite

Offers the lowest weight and best portability which makes it perfect for frequent travel without compromising the training.

  • Enhanced Portability
  • Holds 1-4 Flywheels
  • Built in kMeter
  • Weighs 9.5 kg
  • Starting at €2 300 / $2 665
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kBox4 Pro

Our premium kBox model with the greatest versatility and largest performance area. It’s ideal for sports teams, premium fitness clubs and physiotherapy facilities.

  • Largest Performance Area
  • Holds 1-4 Flywheels
  • Built in kMeter
  • Weighs 15.5 kg
  • Starting at €2 990 / $3 465
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The kPulley2 is the ideal horizontal solution for improving strength by offering flywheel training for rotational and pull exercises.

  • Horizontal Model
  • Holds 1-2 Flywheels
  • Built in kMeter
  • Easy to assemble
  • Starting at €1 890 / $2 190
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