“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.


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 Inno-sport.net and Wannagetfast.com web sites with athlete coach Dan Fichter. He also had the opportunity to work occasionally with some Olympic sprinters and other professional athletes.

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