How the kBox Helps Dutch Physiotherapist Lotte Lafeber

Flywheel training is increasingly being used for rehabilitation and physiotherapy, and the world’s most innovative country in this applying this is probably the Netherlands. One of the many skilled Dutch flywheel physiotherapists is Lotte Lafeber in Rotterdam.

Fredrik Correa reached out to Lotte to learn more about her involvement with flywheel training and how she uses the kBox with her patients. She generously agreed to share her experience, for us all to benefit from.

Lotte Lafeber

How come you wanted to be a physio?

I’ve always wanted to work in health care since I was young. When I found out that with physiotherapy you can combine working in health care with sports I chose this field. In the work you have a lot of contact with the patients which I like. Working togther with a patient to reach the goals you’ve set up together is a very thankful job.

Tell us about your current work as a physio?

I’m working as a physiotherapist for two days a week at Praktijk voor fysio- en manuele therapie ‘Groothandelsgebouw’ in Rotterdam and for two days a week at Fysio Effect in Rijswijk. We see all kinds of patients and their problems varies from back pain and neck pain caused by working to much at a desk to injuries during sports. Since I’m doing a master in sport physiotherapy I’m focusing on the patients with injuries related to sports. So for example runners with knee injuries or rehabilitation after an operation like an anterior cruciate ligament (ACL) reconstruction.

How did you come in contact with flywheel training?

We were looking for a new and innovative way of strength training. We came in contact with the company Fyzzio and they advised us to try flywheel training. So we purchased a kBox combined with SmartCoach to the clinic in Rotterdam.

What problems or difficulties do you find the kBox solves for you in rehab?

While training with patients I always try to use the most functional way. Mostly the goal in rehab is not to get as big muscles as possible, but to be able to use the muscle in the right way during your normal activities or during sports. During normal movements your muscles are contracting concentric, eccentric and isotonic. With most strength training you’re training the concentric contraction and a bit isotonic but the eccentric contraction is less involved. With the kBox you can make sure you use all three of them. So this makes it a very functional way to train the muscles and it simulates the real sports activity.

Praktijk voor Fysio- en Manuele Therapie "Groothandelsgebouw"How do you think the kBox works as tool in rehab and then crossing over into regular training?

It helps that you not only focus on the concentric but also on eccentric contraction but also that you can analyse your training using the feedback. You can make the results clear to your patients by showing the progression curve and also expose asymmetries in strength between the left end right leg.

Are there any situations where you believe the kBox is extra beneficial?

I often use the kBox with people with knee problems where I see a lot of positive results. The feedback I get from patients is also positive and they appreciate this new form of training. Because of the clear results presented via SmartCoach they are very motivated to achieve maximum with every repetition. We’ve put a laptop next to the kBox so not only we but also the patient can see it.

Can you tell us about any special cases where you have used the kBox and what the outcome was?

I will tell you about someone with patellofemoral knee pain. In her case the condition of the cartilage between patella and femur was decreased. With normal activities she didn’t experience pain but with sporting the pressure on the patella increased and pain was revealed in the knee. With the kBox we trained the strength of the quadriceps, the collaboration between quadriceps and hamstrings and the abductor muscles of the hip to optimize function of the lower-extremity kinematic chain. This in combination with some stability training led to the fact that she is sporting now with no pain at all.

Do you have any tips for other physios looking at incorporating flywheel training in their clinical work?

I would like to advise them to do so. It is a very effective way to train with your patients. Besides that, the kBox itself is not that big. So if you don’t have much space in your exercise room for big devices the kBox is the good way to go.

Last, what are your personal plans in the next year looking at your professional life?

I would like to develop more in the sports field of physiotherapy. During my master, the coming three years I hope to learn much more about training and rehabilitation. Also I would like to focus more on prevention of injuries. With an analysis you can often already see where weak points are. When you start training that before it results in an overload at that point, you can often prevent the athlete from getting an actual injury. And the kBox will be a helpful part in this.

That wraps it up, thank you Lotte for contributing and good luck in your future studies and professional development!

/Fredrik Correa, M.D., co-founder

Learn more about the applications of flywheel training in rehabilitation.

Henrik Petré Joins Exxentric to Develop Education for Flywheel Training

While we have developed and spread the leading product offering for flywheel training worldwide, we have also wanted to add a strong education offering. Today we take the first important step towards this goal, by adding the experienced strength coach Henrik Petré to the Exxentric team as our new Head of Education.

Henrik PetréHenrik is deeply rooted in performance sports, with a background as a professional ice hockey player at the highest level in Europe for 15 years. During the past six years he has worked with ice hockey players from several NHL organisations as their strength and conditioning coach during the summer off-ice training.

Alongside his professional career, Henrik has studied medical science and sports science and has a B.Sc. degree from the Swedish School of Sport and Health Sciences (GIH) in Stockholm, and he continues to study on his spare time towards a M.Sc. in sports science.

As a coach, Henrik is a long-time flywheel training expert, and he brings deep personal experience from the benefits of the kBox in performance sport. In his own words:

“I’ve been training my players with the kBox for the past five years and I have seen great development of strength. The kBox is used in both the concentric and eccentric phases focusing on hypertrophy, maximum strength and power. The ability to add load and overload at angles customised for the specific requirements of the sport has made the kBox invaluable for me in my work with elite ice hockey players.

I see the kBox as a perfect complement to the more traditional training with barbells. The versatility of the kBox is fantastic and it’s safe and suitable for young and old, elite athletes and amateurs, performance sports and rehabilitation. Only the creativity and skill of the practitioner limit the use of the kBox.

In my role at Exxentric I look forward to supporting and helping our current and future users to develop in their professions. To be a part of the Exxentric team and continue to spread the message about flywheel training is going to be fun and inspiring.”

To learn more and connect with Henrik, see his profiles on LinkedIn, Instagram and Twitter. Please join me in giving Henrik our warmest welcome to Exxentric!

Erik Lindberg/Erik Lindberg, CEO

The kMeter Feedback App Updated with New Perks

We couldn’t imagine how much people would use the kMeter feedback system, now an integral part of the kBox3. Following further development work and feedback from the key users, we can now release an updated version 1.1 of the kMeter app.

The kMeter 1.1 comes with several new perks, including:

kMeter 1.1 - Screen 1Real-time force feedback

In the previous version you could choose between average and peak power in the real-time graph view, but now you can also get your force estimation rep by rep. If you are doing hypertrophy or max strength work, force feedback is probably more interesting – and now you got it, right under your thumb. Enjoy your Newtons!

kMeter 1.1 - Screen 2Power / bodyweight

By adding your bodyweight in lbs or kgs in the setup you now get your peak power divided by bodyweight. This gives you an easy way to compare between different users, as well as to follow an individual user undergoing weight changes. Peak power isn’t really telling you anything if you don’t relate it to bodyweight because weight and body composition is determining performance outcome in all movements. For users dropping in weight it’s also important to validate that their power / bodyweight is increasing despite their maximal power output might go down a bit.

kMeter 1.1 - Screen 3Connect button on startup screen

Not a big thing but now it’s even easier to connect the app to your kMeter module. At the startup screen just press connect and if your kMeter is activated and your iOS unit has bluetooth enabled you’ll be hooked up in no time.

Battery check

Now we’ve added a low battery warning so your kMeter doesn’t go out of juice before you do!

In addition to these perks we also made a couple of minor fixes to improve the app further. If you already have the kMeter Module for your kBox, go to the App Store to download the new app for free.

We have great plans for the kMeter app and many things we want to add to it. Which ones we prioritize is a lot up to you, our users. Give us a shout out on Twitter or Facebook or drop us an email if you have any questions, thoughts, ideas, feedback or if you found a bug. That can only help us improve and make the most wanted improvements and updates as soon as possible!

Happy DOMS!

/Fredrik Correa, M.D., co-founder

Is Eccentric Overload on the kBox3 Safe?

Safety is a key concern in heavy strength training in general, and in eccentric overload training in particular. How does flywheel training differ from conventional methods in this regard – and how is it safer? Read M.D. Fredrik Correa sharing his thoughts on this important subject.

Super Strength Show badgeWith more and more kBoxes out there the number of people using it increases at a fast rate. Some of those use it for eccentric overload training which is a great purpose for the kBox and a very important feature of flywheel training. Eccentric training is a known promotor of hypertrophy and strength (Roig et al 2009) and it’s also injury preventive. Eccentric overload training also has been shown to be more effective to transform strength gains into performance gains in trained subjects compared to regular CON:ECC 1:1 training (Friedmann-Bette et al 2010).

Coming on the Super Strength Show with Ray Toulany recently we talked about this type of training and one of the questions was, is it safe? This is a valid question but being on the show with a limited time to answer it basically boiled down to me saying “yes”. However, with the show just released I want to take the time to elaborate on this subject here.

Eccentric overload with kBox Squat by PhD Mike YoungCompetent high speed #kBoxSquat’s performed by PhD Mike Young, using his arms and the squat rack in the concentric action to achieve #eccentricoverload on the descent.Learn more: #flywheeltraining

Posted by Exxentric on den 7 juni 2015

First of all, heavy resistance training and basically all maximal or near maximal training do pose a risk, however you do it. Training can also be maximal in different ways with maximal speed, load or time (to exhaustion or fatigue) and all of them pose different risks of injury. In the short perspective you can have a trauma or acute overload like a muscle tear. Maximal training also poses a risk in the long term with constant heavy loads or repeated trauma that could lead to overuse injuries, stress fractures and other nasty stuff. So to say if the eccentric overload training with the kBox really is safe we have to establish a baseline risk of complications related to that type of training with standard protocols.

The next problem, what is the standard protocol? Comparing the rather fast eccentrics with the kBox is problematic since traditional supramaximal eccentrics is done (if done at all due its impractical nature) using spotters and often very slow. Forced reps is often faster than the supramaximal eccentrics but also submaximal in terms of load in comparison with supramaximal kBox eccentrics. In the end all those eccentrics can be done in different ways, kBox eccentrics can be slow too, barbell eccentrics can be faster and so on. So in terms of load and speed it’s difficult to say what is standard and what risk it does pose, but logic tells us that higher loads and higher speed would increase risk of injury, but how much is unknown.

Overloaded squat-assisted single leg RDL:s by PhD Mike YoungPhD Mike Young doing some overloaded squat-assisted single leg RDL:s using the #kBox3.By pulling with two legs in the concentric phase using a stronger movement pattern, Mike “loads” the flywheel for a massive eccentric overload in the single leg eccentric phase. This is great for performance enhancement, and research strongly indicates that eccentric focused hamstring training helps prevent injuries.Learn more about #flywheeltraining:

Posted by Exxentric on den 25 juni 2015

Moving on to the things around the training, the setup. With the kBox you can be connected with the harness which to some looks dangerous. However, if you stop pulling in the CON phase you are immediately unloaded since the force depends on you pulling. The flywheel will continue to spin and unwind the belt from the shaft. If you are close to the end of ROM in CON or even in beginning of ECC you can get and instant unload as well just by pulling the quick release on the snap shackle connecting the pulley to the harness. The flywheel will continue to spin and rewind the strap and pull in the pulley but you are disconnected and unloaded. Quick release doesn’t need a spotter, you can do it yourself and you don’t have to rely on a – sometimes unfocused – spotter.

Comparing to heavy barbell lifts like the squat when you most definately need spotters, sometimes even multiple spotters, to lift the weight and probably in ECC too for safety. That involves more people, communication and timing in help and to my experience this is posing a higher risk of injury if you need to suddenly abort your lift.

Back on the kBox, when doing deadlifts using a bar you can just drop the bar at any point and basically the only injury you can get is dropping the bar on your foot, which is less than 1 lbs from about 59-100 cm height and if you get seriously hurt from this you are probably not looking at playing professional rugby in the future with that glass foot. You could theoretically get the strap around your foot and have it squeeze your foot but that would require a very strange positioning and a wreckless technique. If you have a spotter using the kBox it’s even safer since your spotter can at any time just put his or her sole against the flywheel and stop it in a second.

To sum it up I think the kBox offers SAFER overload despite that you can work at supramaximal loads at higher speeds. This is because you aren’t lifting any weights that can fall down and that you can quick release from the pulley or drop the bar at any time or have a spotter that can easily stop the flywheel. Is it completely safe? No probably not since your dealing with high loads. So take necessary precautions and make good preparations. Warm up, know your drills, prepare yourself with what you should if you need to abort and increase overload gradually over time. Then you will do alright.

Happy DOMS,

/Fredrik Correa, M.D., co-founder


If you have comments on this or other opinions on eccentric overload training and/or flywheel training, please feel free to comment this on twitter (@fredrikcorrea) or contact me privately at DS

Get a Private kBox 3 Demonstration at the ECSS Congress in Malmö

Are you attending the 20th ECSS Congress in Malmö? This Friday, there will be opportunities to get a private demonstration of the kBox 3 with the new kMeter feedback system by our co-founder Mårten Fredriksson.

The demonstrations will take place at a private location within close walking distance from the congress, and are of course free of charge and without any further obligations. If you are interested, please contact Mårten directly at or +46706032912, or through our contact form.

Mårten FredrikssonMårten is one of the co-founders of Exxentric. He has a B.Sc. in Sports Science and Physical Education from the Swedish School of Sports and Health Science in Stockholm (GIH), and has worked as an ice hockey coach for over 15 years with teams on the highest level and also participated at eight world championships and two Olympics as strength & conditioning and tactical coach.

Flywheel Training Beginners’ Mistakes and How to Avoid Them

The kBox was built with safety and ease of use in mind, and there are only five simple rules that the user needs to bear in mind to start working with it. Here is Dr Fredrik Correa’s advice for a proper start with flywheel training.

The kBox is now being used in performance sports, health and fitness and rehabilitation with increasing popularity. Despite it’s small size and neat design, make no mistake: It’s a powerful tool that can give you the strength workout of your life, but it must also be handled correctly to not risk causing problems or even injury.

Fortunately no serious injuries have been reported, but as the kBox gets more and more popular and widespread, we have seen new users taking potential risks, that can be easily prevented. Here is a list of some common usage mistakes on the kBox, what can happen and how to minimise risk of any injury and damage to your device.

1. Falling backwards during squats

falling backwards during squatGetting a more accessible way of doing squats with higher loads, less dependent on form and ability to get eccentric overload were the main reasons for us to start develop the kBox from the beginning. kBox Squats is still probably one of the most common exercises performed with the kBox among everybody from elite athletes to patients or seniors in rehabilitation.

The thing is that when you try to decelerate the flywheel and reverse it to go up in the concentric phase the energy of the flywheel can shock you. In this position many tend to lose balance backwards the first time they push a little harder in the previous concentric phase and get the pull sensation in bottom of the eccentric phase. However, users rarely fall backwards and it just takes a couple of reps to get the hang of it, no worries, but it’s good to know so you don’t frighten your client with your new toy.

What you are doing wrong? You are unaccustomed to the eccentric pulling at the bottom of the squat.

What happens? You tend to lose balance backwards and might fall or get a feeling that you are about to fall.

How do you avoid that? Just by knowing there will be a hard pull you can be ready for this. Remember that the kBox is alive, it’s not a dead weight. Work with a partner or coach standing beside you ready to support you with a push in the lower back if you tend to lose balance. If you work without a partner you can put the kBox against a flat wall and let it catch you or just have it as a security measure in the first couple of sets. After a couple of reps you will get the hang of it.

Using a partner for safety: watch video.

2. Stopping in the top position or getting off when the flywheel is rotating

how to stopThe kBox is alive. All the energy you put into the flywheel’s spinning motion will come back at you after you reach the top position. You decelerate the flywheel in the eccentric phase where at the bottom it is standing still for a second before you go up again in the concentric phase. This means that the stopping position is at the bottom where the flywheel has none or low rotational energy and this is where you should stop, not at the top where the energy is maximal.

What you are doing wrong? You extend all joints in the top position (in the squat for example) and stop or get off the kBox while the flywheel is still rotating.

What can happen? You can hyperextend you knee primarily and also get a high pressure on your knee joint. If you get off the kBox at the top, the spinning energy of the flywheel will retract the drive belt and since it’s not being held down by your bodyweight it will get off the ground and end up hanging in your harness.

How can you avoid that? Never stop in the top position, especially not in leg exercises using the harness. Use the snap shackle for a quick release if you need to unload yourself fast. For inexperienced users you can limit ROM so they can’t extend fully and diminish the risk of them hyperextending. When stopping, decelerate the flywheel in the eccentric phase until a complete stop at the bottom and then get off the kBox.

How to stop and get off: watch video.

3. Connecting the harness the wrong way

wear harnessThe harness is made so it will equalise the pressure on the shoulders and give a much more comfortable experience when training. If in an upright position the pressure will be over the shoulders/traps and if you are a bit leant forward the pressure will be over the lower back so you always have a short lever between the force and the lower back so there is always a minimal torque on the lower back.

What you are doing wrong? You are twisting the harness’ ends the wrong way when connecting.

What can happen? The edges of the harness will cut into your thighs. This can be unpleasant but not dangerous.

How can you avoid that? Connect the harness the right way by turning the harness’ ends inwards.

How to wear the harness: watch video. How to connect the harness: watch video.

4. Getting unnecessary wear on the drive belt

avoid wearBasically the only wearing part of the kBox is the drive belt. To allow you to do a lot of movements in different planes and angles with a high force we gave you movement freedom, but with that came also a higher risk of wear to the belt. By minimizing the wear the kBox stays safer and you need to spend less time and money on changing the belt.

What you are doing wrong? You are letting the belt go against the edges of the kBox.

What can happen? It wears and you need to trim or change it.

How can you avoid that? By having the correct position you make less wear, make sure you are centered on the line between the shaft and where the belt comes out to the right. Remember that you are working in different planes at the same time, like the S-shape of the squat. If you are aligned perfectly in the top you will be positioned too much backwards at the bottom, so position yourself to get the best “average” position. You can also do a lot of exercises facing the short side, even squats. This way you get minimal wear. Exercises with a horisontal component can give friction belt-to-belt. To get rid of this, elevate the kBox in one end.

Position on the kBox doing squats: watch video. Changing position for smoother belt motion: watch video.

5. Giving up too early

kmeterThe kBox3 is relentless and you can never beat it but that is no reason to quit early.

What you are doing wrong? You are quiting too early, missing out on the last reps on the set or skipping entire sets or just don’t squeeze out the last juice you got.

What can happen? Nothing really. Maybe you can miss some gains in strength and mass.

How can you avoid that? First of all, high-force-beastmode-all out-into-the-wall-training isn’t really necessary for getting the results you need. Sometimes you should give it all you got but for the most time, follow your plan, train, eat, sleep and let the results come. The kBox is very effective with it’s variable resistance and higher eccentric loads so you don’t have to do all that volume, all the time. Remember to pace yourself if you are doing multiple sets with higher rep range so you don’t overdo it in the beginning of the first sets. Use the kMeter to limit yourself because the kbox will pull you down and make you go harder and harder if you are not monitoring your load.

This being said, if you aren’t prepared to do a serious workout, don’t use the kBox. Have a Zumba or something.

See the kMeter in Action: watch video.

Happy DOMS,

/Fredrik Correa, M.D., co-founder


Watch the full kBox introduction playlist here, it’s just about 10 minutes long (including the above mentioned videos):

Using the kBox to Rehabilitate Late Stage Tendinopathies and to Prevent Recurrent Injuries

Performance physiotherapist Adam Lovegrove is a long time user of the kBox in his rehabilitation work. Having ordered the kBox 3 and kMeter he published this review, which he gratiously agreed to let us share with you here.

Adam Lovegrove's gymFor the last 12 months I have been using a kBox flywheel training device as part of my strength training programme.

I first came across flywheel training on a podcast by Dr Peter Malinares on tendinopathy rehabilitation. The way it works is you accelerate a flywheel(s) and then have to eccentrically work to decelerate it. The load encountered in each repetition is based on how hard you initiate the lift and accelerate the flywheel. This means that every repetition can be a maximum effort. This is especially the case if you perform a quarter squat with the upper body exercise to increase the acceleration which in turn increases the eccentric work required to decelerate the flywheel (believe me this makes it very intense).

The facts that each repetition can be a maximum effort and the eccentric loading is far greater than conventional weights means, in my opinion, it is a superior strength training method than free weights or machines. However having said that free weights are probably more effective if you are doing explosive, ballistic, weightlifting exercises.

In addition to using the kBox myself I also use it as a physiotherapist to rehabilitate late stage tendinopathies and as a maintenance tool to prevent recurrent injuries. This is very relevant to me as there are studies showing a link between eccentric hamstring strength and decreased injury or recurrence of injury (Askling et al 2003).

Exxentric have recently introduced their new kBox 3 and having watched the videos on You Tube I decided to upgrade my old kBox for the newer version.

The kBox 3 improvements

I have already written a review of the older version so here I will focus on the new innovations that Exxentric have added to the new machine and offer my opinion on them.

Firstly the length adjustor tower has been removed and replaced with an automatic adjustor that you can operate with your feet. This is simple to use and the main reason why I chose to upgrade. It means you can go from lower body to upper body in a superset format without delay and makes your training more time efficient.

The footprint of the machine is also slightly larger, although this did not affect me taller athletes with larger feet will benefit.

The machine also feels smoother when performing your lifts which in my opinion is quite an advantage.

Overall this machine is a considerable improvement on my original kBox and although expensive I think additional training strategies that can be applied and smoothness of movement make it a worthy investment.

The kMeter completes the kBox

Since initially writing this review I have now purchased the kMeter and accompanying app. The kMeter connects to the kBox and is linked to your iPhone or iPad via Bluetooth. You enter the number of flywheels being used so the inertia can be calculated. You then get immediate feedback of the force you are generating when performing your reps. The feedback also provides average concentric and eccentric power measured in watts and average force measured in newtons. You can save all the information for your training diary.

In my opinion this completes the kBox as training device. You can now receive instant feedback so you can monitor your progress, and evaluate your training status.

The fact that many health clubs appear to be incorporating areas for “alternative training” devices such as Bulgarian bags and Battle ropes. I am sure it is only a matter of time before the kBox becomes a feature in many health clubs.

Reference: Askling C, Carlson J, Thortensson A 2003 Hamstring Injury Recurrence in Elite Soccer Players after Preseason Strength Training with Eccentric Overload. Scandinavian Journal of Medicine and Science in Sports 13: 244-250

Adam Lovegrove has 20 years experience as a personal fitness trainer as well as 10 years experience as a physiotherapist. He has a Master’s degree in neuromuscular physiotherapy, specialising in movement control and rehabilitation as well as kinetic control movement therapy. He is currently studying for a second masters in strength and conditioning. Adam uses the kBox for both strength and rehabilitation purposes.

Learn more about using kBox for rehabilitation, or contact us.

“The price isn’t cheap but the value is huge.”

A strong new review of the kBox 3 was posted by coach Drew Cooper on the highly regarded FreelapUSA blog yesterday. Exxentric co-founder, M.D. Fredrik Correa read it with interest.

kBox 3People are purchasing the kBox 3 at an increasing rate all over the world, which is fun and stimulating. But being more a of creative idea-guy myself – a coach at heart and maybe not a businessman foremost – the greatest recognition for me is to get feedback from our users. End-users like gym-goers, patients or athletes, or coaches, performance directors, therapists or doctors, all have their personal opinion and experience with the kBox. We always want to take part of this experience to further improve our product and concept.

Drew CooperOn this theme it was with great pleasure I read a review of the kBox3 yesterday, published on the FreelapUSA blog and written by Drew Cooper (CSCS, BS Kinesiology). Drew has been active in posting training videos from his sessions with different clients he works with in his three-car garage gym. Reading the review, I can really feel how the kBox suits Drews needs and how it improves the training for his customers. Like no other equipment the kBox offers heavy leg training and overload training in a safe, less technique dependent and more ergonomic way. All this packaged in a light product with a small footprint. I’ve have written about this before but in Drew’s story about the kBox it becomes so clear:

“It offers a unique way of training certain qualities such as high force with high-velocity eccentrics, larger times under tension with these specific muscle contraction regimes, improved speed of hypertrophy gains, and orthopedic safety—all with one piece of equipment with a small footprint.”

In terms of training physiology I like that Drew is talking about the fast eccentrics. Look up eccentric training on google and 9 out of 10 posts show really slow submaximal or assisted maximal reps, so far from performance you can come when in reality the eccentric work is often a fast deceleration in the stretch-shortening-cycle primarily like landing after a jump, change of direction and so on. If you look at the force-velocity curve and realise that the eccentric force produced is even higher at higher velocities you can understand that this is the way to work to really engage your neuromuscular system for improvement.

To sum up I wanted to highlight the essence of Drew post with a final quote:

“..the price isn’t cheap but the value is huge”.

We have never intended to do cheap stuff but our definite goal is to bring huge value to all our customers and users.

If you have other things to say to us, feel free to send your feedback to us via twitter or email. All feedback is helping us. Positive feedback keeps us going but the negative stuff makes us go in the right direction. Thanks in advance!

Go ahead and read Drew’s full review on

Happy DOMS,

/Fredrik Correa, M.D., co-founder

“Giving Athletes Instant Feedback Changes Everything”

As the launch approached for the kMeter feedback system, we invited the leading US based track coach and strength training innovator Chris Korfist to try it with his athletes. Here, he generously offered to share his thoughts with us.

One of the big jumps that I made as a track coach was my purchase of an electronic timer. After suffering through some lesser systems, I settled on a Summit timer and two Alge beams, wired. I now had instant feedback on how my athletes were running.

Giving athletes instant feedback on how well they do changes everything. From a psychological standpoint, it encourages flow in a workout. Thanks to Mihály Csíkszentmihályi’s work,* we know that instant feedback encourages individuals to improve faster. It also gives athletes the feedback to see if they are improving or not, which further encourages a positive training environment. And for coaches, it also helps to see if what you are doing is improving your athletes’ abilities.

What happens in the weight room?

The problem for a number of years was that while timers could help your athletes on the track, what happens in the weight room? Max weights are great but not always conducive for all phases of work in the weight room. If coaches are concerned with power output, we know we need to work at a much lighter range. I started with the MuscleLab and progressed to GymAware. Both great but we know that using barbells is not the best method of developing power in the weight room due to lack of eccentric activity.

Enter the kBox. Everyone who has tried the kBox will agree that after using it, traditional barbells feel like “dead weight”. The kBox feels alive. But the problem is how to quantify what you are doing on the kBox. That problem was solved with the new app that measures everything that happens on the kBox – the kMeter.

Visual response is immediate

The kMeter module that attaches under the kBox uses Bluetooth to connect to your iPad, IPhone or other iOS device. I use a HDMI cable to connect the iPhone to a TV so the display gets much larger. So, as the athletes are exercising they get immediate feedback which they don’t have to search for on a small screen. Visual response is much more immediate than a coach yelling out numbers.

I set the number of reps and weight. There is a 2 reps countdown to get the wheel moving and then the big beep, it is go time. As they exercise, a graph and number show their output. If you thought the kBox was difficult before, wait until you put a number on your effort. After your last rep, a new screen pops up and shows a whole range of info, which includes average power, which is displayed while exercising, concentric and eccentric peak power in Watts, average overload, energy, reps, rep time average, and estimated force in Newtons.

Explosive athletes ramp up power

kMeter results croppedSo, I have been recording outputs for my athletes with the smaller flywheel (get better power output). While it is fun to have competitions between athletes, it is more interesting for me to make connections between what people can do in real life athletics and what they are putting out in exercise.

So, if an athlete generates x Watts on a kBox, he can also run x time in the 40 m or jump x inches in the vertical jump. My first observation is that my more explosive athletes tend to generate more power as the set progresses. So my sub 30 inch vertical usually hit their best number early in the set and sometimes completely collapse before the set has ended. Their top rep will be 3. The more explosive athletes continue to ramp the power, so their best reps are at the end. I am guessing what happens is that they can convert the eccentric energy into concentric better and continue to ramp up the output. They usually hit their peak by rep 6-7.

Also, the weaker guys can’t take that much eccentrically and collapse or slow down or lose their groove. So, someone who falls into this range may have a concentric average of 836w and eccentric average of 858w and an overall average of 620w. Their vertical jump is 24.4 inches. An athlete like this would benefit from eccentric work with weights, or an overload on the kBox, by helping him standup quickly (assisted) and getting him to absorb the force. On the other end of the spectrum, I have an athlete who puts out 1824w concentrically and 2194w eccentrically with an average of 1378w. He has a 37 inch vertical jump.

The concentric−eccentric relationship

KorfistI think the most interesting aspect of the kMeter that I have found is that even though someone’s power may not be that great, it is more about the relationship between the concentric and eccentric and this is something that correlates to athletic ability. For example, I have an accomplished high school distance runner who has a concentric peak at 710w but eccentric is 890w, 543w average and 23 inch vertical. While not as fast as a sprinter, he does very well at what he is trained for, distance running. The athletes who lack the eccentric strength are not “athletes”, meaning they are not smooth in movement.

I also use GymAware for my traditional weighted movements and have found that as athletes’ kMeter readings improve, so does their power outputs on the GymAware. I usually mix the two during a workout and add some movement that gets them off the ground. So, if we are doing single leg work, it would look like kBox single leg squat, GymAware single leg squat to single leg jump off a box.

Chicago Speed Clinic

As the weather has warmed up here in Chicago, I will get an opportunity to match kMeter reading with running times and try to make some more correlations between the two. If you want to visit Chicago this summer, we are hosting a Speed Clinic on June 19-20. For more information contact me at

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.

Introducing: The kMeter Feedback System


Today, we are happy to announce the first shipments of our new kMeter feedback system, for accurate monitoring of power and energy performed by kBox flywheel training users.

The kMeter system is developed to fit the fundamental feedback needs and budgets of professional flywheel coaches, physiotherapists and fitness facilities, as well as each individual athlete and user of the kBox.

We believe that the kMeter will change the face of flywheel training. It is an important milestone for Exxentric, where we move from only producing flywheel training equipment, to including also a new software based feedback system.

Why feedback?

Training feedback is essential for many reasons. You need a feedback system to see where you are at. From that starting point you can set a goal and make your own program. During the training period the feedback can help you adjust your training. To evaluate your training you need feedback to see how far you have come. Feedback can also be used to limit an athlete or patient in rehab after injury or pacing before an event.

Many are lead to believe that they know what they are doing in the gym just because they know the number of kgs or lbs they put on the barbell but this knowledge is not sufficient. Kgs and number of sets and reps can be used mainly to quantify training volume but that really doesn’t say much about intensity – for that we need to know force and power during training.

The kMeter system

kMeter Module

The kMeter system consists of two parts: The kMeter module is a bluetooth transmitter which connects to the existing sensor socket on most recent kBoxes. The kMeter app is developed for iOS devices and is available for coaches and physiotherapists as well as users.

Measuring force and power accurately is not trivial, and the kMeter system has been in development for several months. The development team has included individuals with decade-long experience of building flywheel training devices, as well a Ph.D. in Aerospace Engineering and a M.Sc. in Engineering Physics, accomplished in sports app development.

kMeter iconThe kMeter system presents average power per rep, and also peak power in both concentric and eccentric phases to determine eccentric overload. The power data is exact and consistent. Number of reps, rep time and energy expenditure is also exact. Even qualified approximations of vertical motion (ROM) and force are presented. For a full presentation of the functionality, watch the video below.

An important aspect is the system’s backward compatibility. Existing kBox owners can connect the kMeter, as long as the kBox is equipped with a sensor.

Now shipping

As of today, the kMeter app is available to download for free on the App Store. The kMeter module is ready for delivery, priced competitively at EUR 390 plus shipping and taxes. Contact us or your local reseller to place your order.

We hope you’ll want to share your results using the “#kMeter” tag. We’re excited to see who will be able to show the highest power metrics on the kBox!

Erik Lindberg

/Erik Lindberg, CEO