From the Exxentric Summit: The kBox Power Test

Today, we are publishing the kBox Power Test protocol. As presented at the Exxentric Summit, the kBox Power Test is essential to secure comparable power values between users and over time. Here, Fredrik Correa presents the background.


kBox Power TestPower training is essential for athletic performance. For improvement we need measurements. At the Exxentric Summit, I presented our kBox Power Test protocol for 4 RM squats in this purpose (you can download the slide deck here). Now, the protocol is also published on our website as a guide for kBox users.

With the kBox Power Test we offer a standardized protocol to test your users to get comparable and reliable data.

Many of our users have done variations of this and we have to played around with this over the years. Since we launched the kMeter feedback system we have had a great tool for easy and accurate measurement but still you need a good protocol. If we all use the same protocol or if the protocol allows for some variation we can aggregate the data in a reference database for everyones benefit.

First, some advice

Before you start testing your users ask yourself why you do it, what will you use the data for and when will you re-evaluate it. All testing should have a purpose. We hope you will find that generating power data for the kBox reference database is one relevant purpose for testing your users.

Do not to throw your new clients head on into the kBox Power Test. Remember to make sure that your users are familiarized with the kBox Squat first. If not, you will get a poor result and you can’t track their progress, and you will probably overestimate the effect from the training you do with your users.

Why 4 RM?

So, why did we chose to analyze a 4 RM (repetition maximum)? Actually you are doing a 5 RM but we don’t analyze the first pre-repetition so we consider it a 4 RM power test.

This is because, as all our long time users know, if you go 100% from rep 1 your best rep will be around rep 3 or even 4. This is due to the stretch-shortening effect increasing the strength of a concentric contraction after an eccentric contraction.

So by going all out but not registering the first maximal rep you go full throttle into the test and have a better chance to really get your peak power values within those 4 reps. More reps would increase the chance of capturing your peak power but will also increase fatigue and lower the average peak power over those reps. The test is designed to give the best chance for high consecutive peak power values with the least amount of fatigue as possible.

What about depth?

If you attended the Summit you know I said that the depth of the squat is free in the kBoxSquat Power Test, just like a counter-movement jump. This is because we want to be able to add all different users’ values into our database and setting the depth would limit the number of users that wanted to do the test.

Weightlifters will do a full-squat and jumpers might prefer quarter squats. Instead of setting a specific depth we chose to set the depth free and suggest the users chose the depth where he can produce the highest power.

If you listened to Sten Kaiser, PhD and Exxentrics physics advisor at the Summit you remember he told us that in theory and increased range of motion increases power. However in a weight bearing activity like the squat you also add a lot of work to be done since you will spend more energy in a longer range of motion which could counter-act the increase power production with increased fatigue.

We have tested a range of subjects, both male and female athletes from different sports and there is no correlation between self-selected squat depth and peak power in our data.

You can help!

Moving on we hope you will find this to be useful tool in your practise. We hope that you will be able to submit your test data so we can put together a reference database. The end goal would be that we could offer reference values from a wide range of users in terms of gender, age, activity level and sports. Let us know if you want to submit your data to our database!

All data will be anonymous of course. By helping us building a reference data base we can make this a really powerful tool for kBox users. Also, as a participant submitting data you will get earlier access to the database when we have started the collection.

So, lets get started – here it is: The kBox Power Test

Happy DOMS!

/Fredrik Correa, Head of Research & Development

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