Interview with Fredrik Correa from Exxentric — part 2

Robert Simonic
Jun 3, 2018 · 10 min read

Here is a second part of an interview with co-founder of Eccentric company Fredrik Correa.

First part of an interview is available here:

1. Are the protocols for exercising same as with lifting weights? I know you lately pushing your 1RM up, can you describe your way for developing strength with FW?

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We are training the same body and physiology doesn’t change with the tool so in general I’d say it’s the same. However, hard work on the kBox is more intense than with weights. Athletes assess their RPE higher and they have more lactic acid after same volume on the kBox and you have to account for that. With maximal work the kBox actually gives you a drop-set with coupled 1 RMs and that is much harder than a straight set of 6 or 8 reps with weights with a more constant load. If you switch over to flywheel training from a protocol you already have, replacing some or most of your exercises with flywheel I recommend to reduce volume with 30–50%, so if you are doing squats 5x5 I’d say 3x5 instead so you don’t need to increase duration between sessions, that will mess up your planning. Then increase gradually, adding reps or sets over 2–4 weeks. If you are in pre-season and can have your athletes being sore or slightly fatigue for a couple of weeks, just make the switch and they will be fine after a while. About my own 1 RM I don’t know if that is interesting to hear about my training specifically but I used the kBox a lot to increase both my squat and deadlift 1 RM, but in slightly different ways. For the squat it was mainly a great tool to increase my strength in the lower portion since you easily can lower yourself and absorb the load deep and hard without having to carry a high load through the whole ROM. It is also a great way to add volume in more barbell specific periods when I use heavy weights and low volume. Then I supplement with a decent volume of kBox Squats since I’m much more confident in pushing myself when I’m tired on the kBox vs with weights. Same thing would be applicable for metabolic training. You don’t want to do BB squats to failure or AMRAP because of the risk of injury (did anyone say crossfit?). However, on the kBox that works great. When it comes to Deadlift for me it has been helping me a lot to activate my posterior chain properly. Low inertia, max power RDLs has been working good for me to set up before heavy lifts. That fast transition and the eccentric load fires up the posterior chain really good. A low volume with high intensity is really helping my slow BB deadlifts to progress. This is in a context when I try to increase my BB 1 RM and with strength being specific and when I also have good access to weights I want to have that in my program. Then I don’t need to do the heavy 1 RM training on the kBox. But if I didn’t have that access like over the summer for example I’d also use the kBox with a mix of medium and max inertia and low volume, heavy fairly slow RT and that works great for strength improvements.

2. Can we do some contrast training with FW and elasticity or shock training? (I just don’t like plyometric word)

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I’m not much into contrast training myself and don’t have very much experience working with it. When I do kBox and BB in the same session for a muscle however I do however do them in different load-velocity zones, sort of contrast training. For example, like above, explosive RDLs in combo with heavy BB deadlifts. Since the kBox allows for fast transitions, in and out of the device it is a good tool if you want to use it in the field or on the track to combine with jumps, sprints, COD drills etc.

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Fredrik performing Front Squat on a kBox Fly Wheel device.

3. Milan did experiment with performing plyometric exercises on kBox, did you experiment with this setting for yourself too? If the answer is yes, how did you do it and what is your opinion on that?

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I don’t know exactly how you did it but I’ve tried it myself but know a few users that do it including one of my co-workers, a dedicated basketball player. Setup we used have been either on our custom made wooden platform over the kBox or attached the kBox to the floor since you need to keep the kBox from coming after you when you jump. You do squat jumps / CMJs on a very lower inertia and long drive belt length so you are able to get some air time. I don’t really now if this qualifies as plyometrics (I’m not a jump coach) but it is much more explosive and fast than normal squatting. I would probably not replace jumping with this in my opinion. I would however consider replacing jumping with a bar on my back with this. The harness makes the impact on the body much smoother compared to a bar on upper back. The option to track the power output with the kMeter is interesting and it also demands a quite high degree of control and balance to be able to perform it. If you want to highlight those aspects in training it can be a good option but I would have my athletes pass a lot of checkpoints in their training before we come to this.

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Eccentric work has a definitive role in rehabilitation. Using Fly wheel after ACL reconstruction. We found this kind of work very useful as it shortens return-to-play time.

4. In your opinion can FW in future replace BBs?

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The short answer would be ‘not replace, supplement’. However, you have to consider the subject and training goals. For a senior citizen that just needs a stimulus to retain muscle mass and maybe build a little strength or a home user in a similar situation without the need to do explosive actions, OLY or sport specific lifts like a powerlifter I’d say the kBox can take care of the most part of their training and together with the body weight exercises they probably don’t “need” weights. So, could be valid for an athlete with a very general need of strength and no specific needs. However, for many athletes the Olympic lifts are very useful, at least the derivatives and even if some of them can be done on the kBox I see the weight having a solid place there still. On the other hand, I’d say no gym is complete without a multi-exercise flywheel device. It adds so many unique aspects of training like constant tension and load and eccentric overload which is hard to come by in traditional gravity-only gym.

5. On what, using FW, coaches must be particularly careful?

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Like everything being careful is good, overcautious is not. I tell every professional that wants to incorporate FW to get to learn the device themselves first. I see many, especially physios actually, that since they consider the kBox to be a device and not a weight (ie barbell) they can just give instructions and use it with a patient without knowing it themselves but the kBox is more like a free weight in that aspect. There is no strict range of motion or bar path and the load can differ a lot from rep to rep depending on intensity and control. I recommend everyone to use the tool for himself a couple of weeks and then start using it with clients. Start with one or two exercises you really like and master yourself and from that gradually increase your exercise bank so you get experience in how people react to different drills and how to cue them. It doesn’t build confidence in the device (or the trainer/coach/physio) if they can’t handle the device themselves and the client will feel uncertain. To be able to give the right cues you have to know how it feels yourself. Less important is the device but still, it is an investment and it need proper handling so learning it so you can teach is a good start. By using it the wrong way you can of course make it age faster or even break and also put your clients to risk. Learn the tool!

Fredrik performing demo on kBox. (source: Exxentric channel on youtube)

6. In a year that I am using FW now I come to some conclusions (based on reading papers, talking with you and my own experineces) now tell me if I am wrong or missed the target. FW devices are particulary good equipemnt for rehabilitation. In training settings, I am using it in the GPP phase when developing connective tissue (anatomical adaptation), before (talking in weeks) doing any sprinting, COD and jumping. But I have some reservations doing it between competition period…?

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Well I wouldn’t have a problem using it in the competitive season but I’d make sure to build technique and capacity for flywheel training in the cycle leading up the competitive period and reduce volume accordingly to not push the athlete over the top a create unnecessary fatigue. If your athletes have built a tolerance for 2–3 overload session a week then can for sure handle 1 session a week with high intensity but with lower volume (per session). Adaptation is fast and you can probably keep the capacity to handle the load with a maintaining session every 2–3 weeks if you can’t schedule it more often.

7. Using FW/ excentric modality devices is quite recent trend in S&C world. How is this supported with science?

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Not enough but we are getting there and the good and smart coaches are leading the way. With the elite coaches adopting in we get more and more anecdotal evidence it works and from the teams medical and sport science teams more and more reliable data comes out and gives the researchers something to study. I’d say the researchers are still behind the practioners but they are getting closer. Now we have a couple of in-season studies on different sports for example like handball, basketball, soccer. I’d like to see more PAP studies and studies on a female athletic population, that is sort of missing today. We also need to see more specific studies on performance in specific sports and studies on specific conditions like ACL rehab, arthrosis etc. Anecdotal evidence from practice looks really promising however, both for the clinical cases and in sports performance. There is one big hamstring injury study start now on elite athletes and I know there is a patellar tendinitis study with good results that hasn’t been published yet. From a pilot I also know that kBox had an excellent result on patients with knee osteoarthritis but more publications can’t hurt. I think we have enough to get started but until we know what protocols are best and how to do them, when and for who there will be some time.

8. Who and where are exxentrics customers regarding national teams, clubs, military…?

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Our customers are spread all over the world. We sold to all continents and over 60 countries so far. We have sold to all different arms of the military, navy, air force and army mainly special forces teams. Fire brigades are also a relatively large customer segment for us. Police not so much yet but in Sweden at least I think the fire brigades are much more organized when it comes to physical training than the police. In elite sports we sold mainly to pro teams but also to multiple national teams but we can’t mention them all, if you want to get an understanding of the variety of users check our social media feeds, those are approved by the users and we are proud to show them.

9. Tell me who was the best skier on the world and the name/brand of skies he did skiing on? Watch out this is tricky one!

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Part A is so easy, Ingemar Stenmark of course. He is a legend over here as you can imagine. He had a really nice quote when a reporter asked him how he could be so lucky after another victory “funny thing this with luck, the more I practice the more luck I seems to have”. About his skis I actually had to check with our CEO, without hesitation he said Elan, I guess that brand is somewhat familiar to you guys.

10. Of course, Elan is our brand from Slovenia, I still ski on them. Too bad they aren’t in world cup anymore. Ok let us finish this interview do you have anything you want add at the end?

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Not really, I think wrote to much already, nobody will get this far in the text anyway ;-)

One thing I could mention is a big thank you to all our users, coaches, physios, patients reaching out to us. Feedback is great and of course we love to hear that our baby can help people but feedback for improvements, new devices, new functions in the feedback app have been very motivating and helpful for us in our work. We couldn’t do this without customers and users! We hope to be able to repay this in the future be producing even smarter and better devices.

Where can people reach you for more information?

People can contact me on:

or @fredrikcorrea on Twitter. (

For media or info I’d suggest or (web).

Thanks Fredrik, I really appreciate your time, willingness to do this interview and share with us your wisdom.

If anybody from our part of the world (Serbia & Slovenia or nearby) want to experience Fly wheel/eccentric training he/she can contact us and we can arrange session, just contact us on social media:

Serbia — Milan Veselinović:

Slovenia — SuperTrening:

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