The Case for Sophisticated Power Measurement

In a fresh article on the Freelap USA blog, olympic coach Carl Valle makes a great argument for the need to monitor performance during training and also to do this in a valid and accurate way.

When it comes to our kBox some people ask how to measure their work, which is a valid question. The answer is the SmartCoach system, which Carl also lists as a top 10 feedback system. The problem is that people I meet often want to relate the results “to my barbell squat in kg”. This is a different thing. My usual response is: “How can you compare if you don’t measure your barbell lift?”

Knowing the load on the barbells doesn’t tell your power output. It depends on the speed and the distance the load travels, and you have to measure this as well to compare. I hope more coaches and athletes pick up this from Carl and start to look at their training in a more sophisticated way, using all the benfits that new technology offers.

I’m also glad to read Carls fine remarks about the kBox, which in his words delivers “an unholy amount of force to the lower body” and that the kBox is the future closed-chain replacement of the Nordic Hamstring Curl. We think so too.

/Fredrik Correa, M.D.

Force comparison between barbell and kBox flywheel squat using force plates and SmartCoach.

Force comparison between barbell and kBox flywheel squat using force plates and SmartCoach.

New Study:
kBox Usage Can Make Swimmers Start 35% Faster

Swimmers that do lunge exercises on a flywheel squat device such as the Exxentric kBox prior to a race get a 35% faster start. This is evident from a new study from the University of Granada, which validates the so-called post-activation potentiation (PAP) protocol.

Georgy doing lunge exercises on the Exxentric kBox.Numerous studies have shown that using a flywheel device results in higher muscular activation and muscular forces during training. As a result, increases in strength and hypertrophy are higher during a flywheel training regimen as compared to using traditional weights.

Can this higher activation be useful in a race context too? The answer is Yes! Post-Activation Potentation (PAP) is a technique to elicit higher muscular force in explosive actions. This has been explained well in an excellent article by sports scientist Bret Contreras:

“The underlying principle surrounding PAP is that heavy loading prior to explosive activity induces a high degree of central nervous system stimulation which results in greater motor unit recruitment lasting anywhere from five to thirty minutes.”

PAP has showed mixed results in studies and the conclusion has been that the protocol (type of exercise, intensity and rest) before performance must be validated. It is therefore interesting to read a new publication from researchers at the University of Granada, who studied two different protocols for PAP before swim start. They compared them first to each other and then to warm-up only. PAP consisted of either three reps of barbell lunges (85% of 1 RM) or four lunges on a first-generation multi-exercise flywheel device.

Results showed that mean horizontal velocity in the swim start increased by 35% with the flywheel lunges as compared to warm-up only and by 18% as compared to PAP with barbell lunges. This flying start gave the swimmers faster times to 5 and 15 meters after the flywheel PAP and this protocol can give the swimmers a significant advantage in shorter events.

/Fredrik Correa, M.D.

To learn more about how your team could use the Exxentric kBox to benefit from these results, please contact us at: or call +46-733-559049.

“The Best Piece Of Equipment That I Have Come Across”

This quote about the Exxentric kBox comes from US based track coach Chris Korfist, who has produced 59 all-state track athletes in the last 22 years. We read his statement in a new article on Just Fly Sports about his work as a sprint coach. We wanted to learn more, so Exxentric co-founder M.D. Fredrik Correa contacted Chris to ask some questions. He was happy to share his views on successful sprint coaching and the benefits of using a kBox.

The Exxentric kBox

Fredrik: In the interview on Just Fly Sports you said that the kBox is “the best piece of equipment that I have come across”. Can you elaborate on that?

Chris: Most equipment on the market is just dead weight. In some cases, it is even less when you add pulleys and other devices that lessens the pull on the muscle. The kBox is more like sport. In most athletic movements, an athlete is required to respond to the force imposed on their body. For example, when running, an athlete has to absorb the force driving the body into the ground by springing back into it. In most cases, that amount is more than two times the body weight. On a regular piece of exercise equipment an athlete won’t experience that force, but he will on a kBox. An athlete has to stop that wheel and reverse it. Put a couple of discs on and an athlete will feel that force.

How do you use the kBox in developing faster sprinters? What exercises do you do?

As I mentioned, we try to get high forces into the athlete and try to replicate that same motion as running or jumping. To do so, we do single leg squats, split squats and regular squats using a variety of belts so an athlete can pull from different body parts. Some people recruit differently based on where the pull is originating, so I designed some other belts to have athletes drive from the muscles that I want to develop. The harness is great but some athletes feel too much back so I have rigged a belt that I can pull from different areas to get the individual to work what I want. We also wave load the different discs with the different exercises. We also do a hip hike for the glute medius muscle which works great with distance runners as well. And we do a psoas muscle knee drive that really gets a great glute/psoas combo. Romanian Deadlifts are great too for hamstring work. We will do RDL and then do a fly or single leg work and do an acceleration.

What advantages does the kBox offer that you can’t get with your traditional tools?

As I mentioned, the eccentric aspect is key to athletic development and the kBox offers the best in eccentric training. The flywheel mechanism is a great way to train reversal strength. You can see someone’s power by watching the wheel change directions.

After using the kBox for some time now, what effect do you see in your athletes?

I use laser timer and jump pad to constantly measure my athletes and I saw bigger gains this summer than I have in the past. I had a larger group of athletes jumping over 32 inches off a mat. And these are high school athletes. We saw similar improvements in block 30’s and fly 10’s as well. I also use a muscle lab to measure output in single leg exercises and have seen an uncommon jump in power output as well.

Sprint speed is crucial in many team sports. What are your basic tips for coaches in other sports when it comes to speed training?

Don’t put too many spices in the cake. Focus on one aspect of an athlete’s development. Bigger, faster, stronger is a myth. And rest is a workout. Let the body fully recover before going at it again. Most people never see what happens as a result of a workout because they get slammed with another one.

What advantages do you see with being able to do the training in the field?

The biggest advantage is to be able to do an exercise on the kBox and then go sprint or start or accelerate or jump. Appropriate rest is needed in between the two. The kBox does cause quite a bit of fatigue.

Do your athletes feel any difference between squats with high or low inertia on the kBox compared to free weights and if so, what do they feel is different?

The kBox feels alive. It is trying to pull you into the ground. A barbell just feels like dead weight. 2-3 plates on the kBox is a great eccentric workout.

That wraps it up guys. Hope you enjoyed the reading! /Fredrik

About Chris KorfistChris Korfist Bio Pic

Chris has been coaching track for 22 years in Illinois, US. He has coached high school athletes at Hinsdale Central, Downers Grove North and York HS, producing 59 all-state track athletes, three individual state champions, two team state champions, three 2nd place team finishes, and two 3rd place finishes. He owns the Slow Guy Speed School which is a gym that focuses on running and athletic development from which other all-state athletes have trained. He used to run the and web sites with athlete coach Dan Fichter. He also had the opportunity to work occasionally with some Olympic sprinters and other professional athletes.

What’s up with Exxentric?

Not much, you might think if you are looking at our frequency updating our news section. It is however rather the opposite. Our sales are rapidly increasing with new new markets appearing all the time.

In may we hosted a flywheel conference, the Exxentric Summit, with distributors, trainers, coaches and researchers from 9 different countries. We got together, shared ideas, research, protocols and had a lot of fun and this was a huge boost for our intensive work in developing new tools for our customers. Here are some pics from the Summit.

Other recent activities have been workshop in rehabilitation with our reference clinic Hela Kroppen in Stockholm and some private workshops and testing session with our newest advance in feedback technology, SmartCoach Encoder and force plates with enables you to measure force in both legs to see force curves during training, measure overload or imbalance between left-right etc. A really nice tool for a lot of our practitioners.
petre plates
Further on we are working hard to deliver all orders before our short vacation. Vacation really means that our factory is closed for a short while. We will still be working with development, handling orders, workshops and so on during that time.
Check back again after the summer so you don’t miss our new stuff that is coming up!

Afraid of muscle soreness?

Muscle soreness is familiar to everybody (Well, maybe not everybody but if you haven’t experienced muscle soreness, how the hell did you get to this post?!). Walking funnily, feeling pain during eccentric contraction (like walking down stairs), and experiencing muscle weakness are all classic symtoms of DOMS, Delayed Onset of Muscle Soreness. Not to be confused with the muscle soreness you feel in the end of a training session when you curl that tiny weight and it feels like you lift a small car, your training partner is screaming in your ear and you just want to go home and cramp up in a fetal position. That’s Acute Muscle Soreness, AMS, which is something else.

Back to DOMS. This all to clear message from our body that we aren’t as fit as we thought, is it any good at all?

Yes, DOMS is great. Read on!

DOMS develops during the next couple of days after a training session, always with the same pattern:

Day 1, “Hey that wasn’t so bad, I thought I would have this sick soreness, I think I’m pretty fit after all”.

Day 2 “Damn, those old glutes and hamstrings hurts as hell. Why can’t Earth be completely flat? All these stairs and slopes are killing me.”.

Day 3 “Mama!”.

DOMS peaks in about 48-72 hours after the training session. During DOMS you can experience muscle damage with a corresponding decreased in muscle function, an acute-phase inflammatory response (CRP for example; C-reactive protein), increased activity of myofibrillar proteins like Creatine Kinase, Lactate Dehydrogenase and Myoglobin. So, what is it that trigger this really unpleasant physiological response in my hard earn muscles? Mainly the eccentric contraction.

Eccentric contraction is when you resist a weight or a force that is elongating your muscle, for example lowering the dumbbell in a curl or lowering the bar in the bench press. One majestic eccentric exercise is the Nordic Hamstring Exercise (NHE). Most people will get DOMS just by watching others do this exercise, check it out here.

In short, eccentric contractions give your muscle a higher degree of muscle damage and subsequently, more DOMS, than concentric actions.

But there is one thing that causes even more DOMS than regular eccentric contractions.

-Say what!?

Yes, eccentric overload. Yes, I know, it sounds like a lot of fun, doesn’t it? Eccentric overload is when the force in the eccentric phase is more than 1 RM concentric. Eccentric overload has been shown to cause even further damage to your muscle, further increase inflammatory response and decrease muscle function even more during DOMS.

Great. But how is that accomplished then? Well traditionally with supra maximal weights and partners helping you in the concentric phase or pushing you down in the eccentric phase (forced negatives), using weight hooks or other inconvenient or impossible, dysfunctional ways. For a list of all stupid ways to get eccentric overload, check here. The smart way however is to use a flywheel device, like the Kinetic Box. By using auxiliary muscles in in the concentric phase and breaking harder in the eccentric phase or by overloading one limb in the eccentric phase after having used both limbs in the concentric phase, you get a high eccentric overload as easy as that! Without weights to break your back, and without partners. With high speed reps you will do eccentric overload as easy as it should be done, unassisted. And you will get the results you deserve.

But hey, what about the huge DOMS I’m getting. Won’t that be destroying my training regimen and break me down completely? C’mon, you are really looking to find an excuses to avoid this, aren’t you? But you see, the thing is that the eccentric training is protective against future training induced DOMS. This is called the repeated bout effect. By doing eccentric training you will not only increase more in strength and muscle mass more, but also protect your muscles from getting DOMS in the future. In training studies with eccentric overload the inflammatory and structural damages is attenuated during a training program with eccentric overload. One session of eccentric training has been show to have a preventive effective for up to 2 weeks!

The good news for you weaklings is that you don’t even have to get DOMS to get a protective effect. By doing low volumes of eccentric contractions with our without eccentric overload, while increasing the load step-by-step you can get the same effect in the long run, without being a cripple 6 out of 7 days a week for a month. Great! The same is seen with older people. Even senior citizens get a good effect from eccentric training. It is actually so that old people even better effect, since they get a higher degree of structural damage from the eccentric training.

Step-by step increase could look like this for the NHE for example (from Iga et al 2012; adapted from Mjolsnes et al 2004):

wk 1: 1 session 2×5

wk 2: 2 sessions 2×6

wk 3: 3 sessions 3×6

wk 4: 3 sessions 3×8.

Increasing load from 10 to 72 reps per week over 4 weeks. And this protocol gave a 21% increase in hamstring muscle torque i 4 weeks!

Well, if you step-by-step increase in training volume doesn’t work on reducing DOMS, studies have shown that coffee reduces pain during DOMS with 48%. Same numbers as for Naproxen.

So, get a kBox and grab a coffee and lets go! don’t fear the muscle soreness!

More posts on effects of eccentric training and flywheel training coming soon!

/Fredrik Correa

Some references:

Fire brigade goes flywheel

We are proud to present that the Greater Stockholm Fire Brigade has chosen flywheel training with the kBox to enhance their training. The kBox is a versatile tool for the firemen since the firemen goes through different phases with regular strength training, performance training and rehabilitation depending on injuries, tasks and performance. We are happy to serve those that serve us! Good luck with the training! To read-up on our former project with Brannkyrka Fire Deparment, check here.


Picture showing the firemen at Katarina Fire Dep. doing some kBox training during the introduction seminar. For more info how the kBox can facilitate and improve your training, contact Exxentric, Sweden.

Entering the UK

PB_Logoscience and football banner

We are glad to be able to announce we now have Perform Better as a reseller in the UK. Perform Better has been around a long time and is the no.1 reseller for performance equipment in the UK. Welcome aboard PB!

We are kicking off our cooperation already in april 30th when Exxentric will attend their booth in the Science and Football Conference, at Soccerdome, London. See you there!

FyzzioKinetic – free intro

Our reseller in the Netherlands, Fyzzio, is arranging free introduction courses to their FyzzioKinetic concept where flywheel and kBox is a vital part. Sign up on their webpage! a free one day course covering the newest forms of training, why miss that? FyzzioKinetic1308

kBox training in the atlantic

Vacation? Now you can try kBox training in the Canary Islands. Visit Training Room Health & Wellness Centre in Las Palmas to get a real nice flywheel work out. Visit their webpage and Facebook for more info.

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kBox workshop Belgium nov 7th

November 7th our reseller Rehab Belgium arrange a workshop, free of charge, for all interested in flywheel training and the kBox. David Bombeke will be talking about how you can use the kBox for different purposes. Great chance to see and try the kBox! Download invitation.

Interview with Dif about their kBox training

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Interview [english] with Djurgarden physical coaches Jordi Gonzalez (A-team) and Victor Stoltz (U17/19) abouth their kBox training. Also show training footage from the in-files training where they combin high-intensity resistance training on kBox with SmartCoach monitoring and high-speed soccer-specific sprints and training. Click image to play or here.

New reseller in Holland

Today we can officially declare Fyzzio as our new reseller in Holland. We have worked closed with them since the start so they already know our products very well and been a great contributor in our development. They will surely be able to help you in the best way if you have questions or want a kBox demo. See our Resellers page for more contact info.

kBox 2.5 is here!

Last week we started shipping our new kBox 2.5. It looks great and feels great. Improvements are for example:

  • new lower tower which is also place towards the edge to give more space on top. It also has a much smoother indexation and it is now a pure pleasure to use it.
  • new design with brown color and black high friction mat that is not getting slippery when wet.
  • hexagonal axis fo easier fitting and changing of flywheels which is much easier now.
  • new reel with lower weight, smaller size and a snap shackle instead of closing hook which gives a deeper motion in the squat for example.
  • flywheels are now 0.025 and 0.050 kgm2 and now much easier to calculate inertia to put into SmartCoach. This also means you only need one light flywheel insted of two as you did before. The old flywheels fit the new kBox so if you upgrade to a kBox 2.5 you don’t have to buy new flywheels.

Pictures can be seen here. Contact us or our resellers if you have any questions.

Flywheel training spreading in soccer

This has been a great year for the kBox and flywheel training in the European soccer leagues. There are now kBoxes with professional teams in the Premier League, Serie A, La Liga, Ligue 1, Russian Premier League and of course, Allsvenskan, our swedish counterpart. Thanks to the dialogue with the experianced and professional staff working with S&C in the different teams we have come up with many ideas for new applications and products, and we are thankful for that.

Do you want to find out why they use flywheel training devices from Exxentric? just send us a mail, check our videos or read the science page.

Cinematic kBox teaser

Cinematic kBox teaser with Jimmy Lidberg, swedish wrestler and bronze medalist at London 2012 that used the kBox is his preparations for the Olympic Games.

You like it? spread it. Want try it? just do it, contact us.

Project Brännkyrka

Project Brännkyrka together with the Stockholm Fire Brigade has started! Earlier studies (1, 2) with firemen have shown that eccentric training is effective in counteracting patellar tendinopathy. In ‘Project Brännkyrka” we want to enable eccentric training in the firemen’s regular training at their fire station in Brännkyrka (known from the reality show on TV4, “112 – på liv och död“). The stations 28 firemen will now work out with the kBox regularly for 12 weeks. The aims of the study is to lower frequency of patellar pain, attenuate training quality, intensity and volume and increase strength in hip and leg extensors. Here is a more thorough description of the study. So far the response have been very positive and we are very glad to be able to work together with Brännkyrka fire station in this project.

Exxentric + SmartCoach = true

We are proud to present our new cooperation with SmartCoach, a innovative and well-established company developing feedback systems for resistance training. As from now all kBoxes will be delivered with a sensor installed from factory and will be ready to connect to SmartCoach different feedback systems. This gives our customers a great opportunity for an even more scientific and exact approach to their training.

Full press release in swedish
SmartCoach webpage

Aftonbladet article about kBox

Aftonbladet interview with CSKA and Swedish national soccer team players Rasmus Elm and Pontus Wernbloom. Elm (translated) “I have had muscle soreness in parts of the thigh I have never felt before”. That’s sounds like the kBox alright.

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Djurgårdens IF goes exxentric

Djurgårdens IF is one of the swedish sport clubs with the longest and finest history with branches into almost every sport known to man. The club resides in the capital of Sweden and their tagline “The pride of Stockholm” isn’t for nothing.

Their soccer team, that plays in the Swedish premier league (Allsvenskan), has brought up a number of national and international soccer stars. As a step in the vision for 2015 to become the best soccer club in the Nordic countries they have changed a lot of things in their training and one thing is bringing in flywheel training. We are happy that we can help them on their quest. Click the image below for video from their training sessions:

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The effects of eccentric training vs concentric on muscle strength and mass

A meta-analysis from 2009 including 20 studies shows higher increases in total and eccentric muscle strength and higher increases in muscle mass and cross-sectional area with high-intensity eccentric training.

“Meta-analyses showed that when eccentric exercise was performed at higher intensities compared with concentric training, total strength and eccentric strength increased more significantly.”

“..the superiority of eccentric training to increase muscle strength and mass appears to be related to the higher loads developed during eccentric contractions”

This is when we say, “told you so!”.

Check out full text article here or abstract at Pubmed here

Eccentric overload -> faster muscles

CSA (muscle size) and force are to common outcomes in studies related to strength (strength training, protein supplements and so on). Since we develop tools for athletes and people that want to perform we like studies that have functional outcomes in performance. This german study showed significant increase in CSA and jump height for concentric + eccentric training with eccentric overload, with benefits over traditional concentric-eccentric training. Another interesting thing is that they saw an increased expression on mRNA for MHC IIX and glycolytic enzymes and an increased CSA for typ IIx fibres. What this means? it means that the overloaded muscle after the training perioded had transformed into a faster muscle! The authors draws the conclusion that this type of training is good for explosive and fast sports. We think they are right.