Choosing the Right kBox Attachments: Harness vs Squat Hip Belt

A few weeks ago, we released the new Squat Hip Belt attachment. This really lowered the entry price of a complete kBox system, not the least for facilities with multiple users. But what are the differences compared to using the more costly Harness? When is the right time for the harness and when to use the belt? Here, Fredrik Correa shares his thinking.

  • The Squat Hip Belt lowers the price point to get started with flywheel training significantly.
  • For maximal power development in squat variations the Harness gives 20-30% higher peak power.
  • The Harness is preferable when doing maximal intensity work with focus on whole body drive, high force and power development.
  • The Squat Hip Belt is perfect in circuits, conditioning and when you want to cycle through many athletes in the same session.
  • For eccentric overload the Harness is clearly beneficial.

kBox Lateral SquatSquat Hip BeltHi, I am back with another never ending blog post and crappy graphs. Today’s topic is “When to use the harness and when to use the belt?”

Getting a fully functional flywheel training system has been, and still is, a serious investment for teams, gyms and personal trainers, not to mention home users. Over the years your confidence in our products and increased sales has made it possible for us to make production more effective and order larger quantities (the major factor behind production cost). This, in turn, has had the effect that a stripped kBox today costs roughly 25% less than a kBox 2 did in 2012. That was also a kBox with fewer features than today, without kMeter and auto-retract for example.

However, while development and production of the kBox itself is a continuos project to increase functionality, safety and durability while lowering the cost there are other things adding to the total cost for the end-customer, like the accessories. When the kBox gradually has become cheaper most accessories have been at about the same price point all the time. Today the total cost of a full kBox3 system with all bells and whistles consists to about 40% of the cost of accessories.

An example of how we address this is the development of our Squat Hip Belt. This a one-size-fits-all belt for €50 which eliminates the need for buying maybe 4 harnesses in different sizes with a total cost of €360. Thanks to the belt you can now get a fully functional Exxentric kBox system for less than €3000.

So, does the Squat Hip Belt really eliminate the need for the Harness? And If you invest in a Harness, what are the benefits?

I put together some thoughts on this both looking at the practical benefits of both products but also differences in power production and fatigue.


When cycling through different drills in the gym or combining kBox drills with sprint and jumps the belt is really beneficial. You can easily wear it when doing other drills, it doesn’t fly around, it’s doesn’t weigh anything. In team and group settings the belt can improve the transition time, especially if every player has their own belt.

Personally I use the belt for other stuff too, like weighted pull-ups, one of my favorite circuit drills that goes perfect together with the kBox. I can also use it around the chest for a decent flywheel push-up. The belt is also one-size, and you can use it with anybody from harness size XS to XL.

Ergonomics and comfort

When it comes to unloading the back, the belt obviously is a little more effective since it only loads from the hip down. On the other hand, at high loads the distribution of the force on the body is softer when using the harness since the force is applied over a larger area.

When doing all-out squats with a good positioning the comfort and also the drive through the exercise is better with the harness. In a leant forward position the harness puts most of the load one the lumbar band so there aren’t much torque on the lower back. However, when going down with a more upright, standard position the spine is loaded. So technique, amount of force and demand for power production can affect your choice here.

Power production

imageIf you want to maximize power production it’s a no-brainer, the harness is way better.

In the graph to the right you can see six trials of the #kBoxPowerTest. I did three using harness (set 1,2 and 6) and three using belt (3, 4, 5) to show the difference in peak power. In these trials I went for a depth beyond my optimal point but I tried to replicate the same range of motion with both belt and harness (further reading on ROM and Peak Power here).

Just to make a point I did the to first two sets with the harness to get a PAP effect (Post-Activation Potentiation) for set 3 but with the belt peak power still was lower. Roughly the same numbers in set 4 and 5 where I also was using the belt. To prove the point I did a set using the harness in a 6th set and then got a higher peak power, actually the highest of all six.

Looking at this it’s clear power production is lower using the belt. Nothing strange really since you can use the drive from the extension of the hip, upper body and even shrugging when using the harness. How much it is, is difficult to say. I’ve seen my own numbers to be around 30% lower using the belt but in these trials it was about 20%. So around 20-30% lower peak power. This is of course crucial to understand if you think about doing the kBox Power Test using belts for all or some of your athletes, you won’t be able to compare the numbers.

Another thing is the eccentric overload. In the squat you might wanna use hip and back extension and shrugging maximal in CON to get a overload for lower limb in the deeper portion of the following ECC phase. For this purpose the harness is way better.

Below you can see CON and ECC peak power comparing Harness and Squat Hip Belt with two slightly different looking graphs.

image (3)image (1)

Range of motion

Not a big factor but the belt offers a slightly longer range of motion in the squat. So if you go for a deep squat, the belt can be beneficial if you want to gain a couple of centimeters in the bottom position.

In my peak power trials I aimed for the same ROM but ended up a little short using the belt (75 vs 72 cm), probably because I felt I couldn’t generate as much force using the belt and compensated a bit with less depth.


image (2)This is not a very strong argument and also maybe logical and not a discussion really. However, since you use less muscle mass in the squat using the belt (more leg dominant) you might also fatigue faster.

If we look at every individual rep over the three sets i did with the harness and the belt you can see a more pronounced drop-off in power production over the set when using the belt. The graph shows average peak power for rep 1, 2, 3, 4 for both settings over the six sets.

This doesn’t have to be bad. My own feeling when I go all-out is that I tend to compensate more with back extension and maybe shrugging when I start to fatigue in rep 3-4 which I can’t with the belt. If there is a lot of compensation this can be both good and bad depending on the subject and the aim with the training.


There are benefits with both the belt and the harness.

For stronger users and athletes looking at maximal power production and eccentric overload I’d say harness is a must since it allows for stronger whole body drive in the motion. With all-out training or really high inertia the belt can be less comfortable.

However, even for athletes there might be a need to target the lower body for specific adaptions, in conditioning or when there are back problems not allowing for load over the spine, and then I’d prefer the belt.

The belt also increases range of motion slightly which can beneficial for some.

So, to get started at the lowest price point without losing to much functionality I’d say the Squat Hip Belt is really good. In a team setting you can do quite well with only belts, but to me the best option of course is to have both. I use harness and belt 50/50 depending on what my program looks like that day.

If you have any questions with regards to the choice between the Harness and the Squat Hip Belt, just drop us an email.

Happy DOMS!

/Fredrik Correa, Head of Research & Development

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