“The fastest drug-free changes I have seen on paper”

Olympic track coach Carl Valle has published an interesting article on eccentric exercises and kBox training, which has already been shared widely. Fredrik Correa has read it with interest – here is his review.


When Carl Valle writes, I’m always excited to read it.

Carl is a US based coach who has produced champions in track & field, swimming and other sports, at every level from high school up to the Olympic level. This in combination with his expertise in performance data and understanding of practical applications of equipment makes him a great source of insight.

I found Carl’s new text a long but good read for anyone working with athletes or strength, both on eccentrics in general and on the kBox in particular. At the end he shares some of his interesting empirical results after a month of testing the kBox. More on that below!

Programming Eccentric Training

Even if you would not be interested in flywheel training for your eccentrics, I think the first general section gives a lot of valuable input about how to incorporate eccentrics in terms of restitution and programming.

Carl and I seem to agree that there is no reason to do “eccentric periods”, or even sessions, since this will give you unnecessary DOMS. Instead you should add eccentric reps in your existing programs, get accustomed to it, then increase the work with complete sets and maybe add some specific exercises like Nordics with a specific aim. Replacing your regular CON-ECC weight training with eccentric sessions in general will only take time away from training, with DOMS or fatigue or even break you down.

My tips for quality eccentrics; Start low, go specific, progress and then rest accordingly.

The kBox Results

We were happy to note that Carl Valle has given his kBox a thorough test ride. And the findings he shared of his month-long analysis were quite interesting:

“The results were very impressive, and the lean mass increase locally to the legs and hips were the fastest drug-free changes I have seen on paper. We hit personal bests in medicine ball throw output and maximal squat tests, but this is again empirical evidence.”

Fantastic feedback by any measure. Also, we look forward to hearing more from Carl as some effects remain to be explained fully:

“What is interesting is the EMG studies paired with the research on IGF-1, Free Testosterone: Cortisol ratio and Creatine Kinase markers. We did more work than usual. The ANS system was disturbed but we rebounded, and the hormones were not depressed but elevated. My guess is that inflammation may be higher than normal, but the gene activation was showing positive protein synthesis. I asked a few coaches and sport scientists, and the mystery was still present, so we will continue to experiment and track changes.”

Choice of Flywheel Exercises

Regarding the choice of flywheel exercises, I want to add that there is much more to the kBox than just the kBox Squat or lower body work. However, it’s a great start and athletes with lower body focus might not go beyond this. I just want to point out this since PT clients, rehabilitation patients, gym-goers or crossfitters can benefit a lot from the upper body drills too, so don’t forget them.

And the kBox is not only about heavy eccentrics either. You can do high volume training or explosive training, just take a look at the force-velocity curve, adjust speed and inertia to match your aims and go.

Thanks for sharing your thoughts Carl, we look forward to hearing from you again.

Happy DOMS,

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

PS. See also my previous post discussing another article by Carl, about power measurement.

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