The benefits of iso-inertial training to build muscle 👌

The use of a iso-inertial device for strength training dates back to 1913 when Swedish researchers published research on muscle physiology using a bicycle ergometer with a flywheel for resistance.

In the field of health and sport, the development of inertial systems was born at the end of the 80s at the Karolinska Institute (Sweden) by professors H. Berg and P. Tesch.  

Due to the loss of muscle mass of astronauts having spent long periods on space stations, non-gravitational muscle work was necessary. Indeed, when you are in weightlessness, it is super easy to bench press at 500 kilos 😉

Since then, these training systems have been continuously improved both in the fields of elite sports and in all sports and fitness practices such as physiotherapy and sports rehabilitation.

Before defining the principles of this bodybuilding technique, you will discover the type of equipment used.

Equipment for iso-inertial training

iso-inertial training at home
Kynett-one pulley

In reality, even if this type of physical preparation is not the best known, it is already accessible for your sessions at home. Companies distribute complete kits with iso-inertial pulleys that can be easily used at home. 

This is for example the case of the site Sports Orthosis where you can order iso inertial sports equipment from Kynett and Handy Gym brands. You will find sets to work all the muscles of the body, at home or on the go, because they are very light while providing incredible resistance.

I will now explain what exactly this is and the advantages of this type of training over traditional free-load techniques such as dumbbells or kettlebells.

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What is iso-inertial training?

Here is a video to help you understand how it works:

Inertial resistance is based on mass or inertia (resistance to change in motion) when speed is applied to a flywheel. The weighted wheel begins to spin due to the action performed in the concentric phase of the exercise, then slows down in the second eccentric phase of the movement when resisted.

To understand, think of the yo-yo of your childhood. A yo-yo changes direction at the bottom, but its mass remains the same. However, we feel a resistance during the movement. Of course, it is weak due to the lightness of the toy, but you can still feel it.

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The principle of inertial resistance

There is a flywheel which is fixed to a shaft from which the traction is carried out. Pulling in the first phase speeds it up. Then the disc would continue to spin but if one has a rope or strap that has reached the end of its stroke, it wraps around the same axis again. 

One can perform a traction in the second phase of the exercise to prevent the disc from continuing to rotate in the same direction.

In flywheels, there is a flywheel attached to a traction shaft. Weights, often in the form of discs, can be added to increase resistance by increasing inertia.

How iso-inertial pulleys engage muscles 

These mechanical structures work the muscles used throughout the movement. The resistance continues in both phases of the exercise, both in the first concentric phase (contraction in muscle shortening) and in the second eccentric phase (lengthening of the muscle).

Therefore, these inertial devices allow a wide variety of exercises at different intensities. In reality, the difficulty adapts to each individual, since it is the strength of the muscle in the concentric phase that determines the resistance during the eccentric phase.

In inertial devices, eccentric overload, sometimes referred to as negative, allows additional stretching of the muscle. Thanks to these equipment, the athlete can perform explosive exercises, which promotes speed and power.


The benefits of iso-inertial exercises

isoinertial exercises with Handy Gym

The resistance of a flywheel is almost unlimited and self-adjusting, since the inertia of the flywheel opposes the force exerted. This suggests that all reps are performed with the correct resistance regardless of user level.

You can therefore train using the iso-inertial device until exhaustion. Indeed, even if your strength decreases with fatigue, the system will adapt to variations in strength over all movements. 

This is very useful because athletes with impaired biomechanical efficiency can still use the device with simple adaptations. This system is also perfect for those who are looking for endurance or who want to lose weight by burning a lot of calories, like in HIIT sessions.

Additionally, there has been a great deal of research conducted on the benefits of eccentric overload (or negative resistance) training for increasing neural and muscle performance, as well as for rehabilitation and injury prevention.

Some of the benefits noted include: 

  • Higher forces are generated compared to traditional concentric action; 
  • Unique neuromuscular activation can be trained specifically;
  • Possibility of specific micro-adaptations to build a stronger musculature;
  • Solicitation of both the targeted muscle and the synergistic (auxiliary) muscles;
  • Strengthening of ligaments and tendons throughout the range of motion;
  • Facilitated rehabilitation after an injury;
  • Increased hypertrophy, therefore muscle mass gain, compared to other forms of training.
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If you are passionate about scientific research on the subject and you are fluent in English, you have a excellent article on the NCBI website regarding the effects of this type of training. He also explains the benefits for muscle rehabilitation. At worst, you can use an automatic translator to understand the main ideas...

Can iso-inertial replace bars and dumbbells?

iso inertial training or dumbbells
Strength training with an isoinertial pulley

To answer the question directly: YES.

My objective is not to say that one is good and the other is worthless. Absolutely not ! Both forms of training will always have their followers and their detractors, but it is worth understanding why isoinertial training has more and more practitioners.

Important differences

There is a big difference between the inertial method and the isotonic action developed in conventional exercises.

Indeed, with weight machines or weights and dumbbells the resistance is constant throughout the entire movement, both in the concentric and eccentric phase. It all depends on the weight taken at the start. You have to move it until the end of your set, even if your strength varies.

In the isoinertial method, the resistance adapts at each instant and is proportional to the developed force. The greater the force expressed by the athlete in the concentric phase, the greater the acceleration and inertia of the flywheel. 

The big advantage of iso-inertial exercises

Iso-inertial training with eccentric overload is consistently proven to be superior to traditional weights for increasing muscle power, strength, hypertrophy, and athletic performance.

The limits of this physical preparation technique

That being said, you must understand that the investment for good equipment is still significant if you have the objective of gaining a lot of muscle, and not just to maintain yourself or reach your ideal weight.

Another disadvantage will be the space available to train at home, and the place where you can fix your pulley. You must therefore choose your inertial pulley system carefully so as not to find yourself unable to use it.

So, it's up to you to see if you should choose this material rather than a bench with dumbbells, elastic bands or some TRX straps. Each solution has advantages and disadvantages that you should weigh before deciding.

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