How the CLAC Method Will Boost Your Eccentric Training

A lot of people want to know what we mean by CLAC and how to do it on the kBox. It’s short for Concentric Load Acceleration Cycles, and those who have tried it wish they never did.


Joke aside, CLAC is the invention of a friend of Exxentric’s, the American world class rower Andy Baxter. Put simple, CLAC is a method for getting dynamic, fast and overloaded eccentric actions coupled with maximal concentric actions. This means high forces, hard work and little rest.

Eccentric Overload

The thing with eccentric resistance training is that you are stronger in the eccentric phase and hence you can overload that phase with about +30% compared to your 1 RM concentric with a range of 20-60% (1) . Overloaded eccentrics (ECC+) are very efficient in building mass and strength (2) and way superior to traditional CON-ECC training. ECC+ training is also efficient in performance improvements in already trained subjects that often can get stronger with resistance training but are having difficulties improving performance (3).

Since regular CON-ECC in flywheel promotes hypertrophy about x2 compared to the same exercise with traditional weights (4) you can start to imagine what would happen if we start doing ECC+ on flywheel devices like the kBox. Yes – gains, gains, gains.

Flywheel Versatility

Apart from the dynamic load of the flywheel you can also get fast eccentrics compared to the slow supramaximal lifts with a barbell. Overloaded squats with a barbell is a quite dangerous and very slow activity. You need spotters and will do probably one rep and rest a couple of minutes. Pretty far from your sport activity, if you aren’t a powerlifter or strongman.

Done on a kBox you can get overloaded eccentrics in a much faster pace and work more dynamically, get higher metabolic demands, get higher forces and more muscular tension and work in much more sport specific velocities. CLAC is the ideal eccentric overload method to achieve all of that. Having fun is optional.

The Concept

The fundamental CLAC concept is to create a series of three consecutive actions consisting of 100% CON and 130%+ ECC, followed by 100% CON. The 2nd ECC phase is with low load going back to starting point. Obviously this requires decreasing the resistance for each rep to adapt to the increasing fatigue of the user. Using a versatile flywheel device such as the kBox, CLAC can be done easily with a variety of excercises, particularly in the upper body.

Let’s take biceps curl for example. You start a concentric action with accelerating the flywheel with your lower limbs, with a squat action. When legs and hip are extended you start curling. At the end of the concentric curl you will have all energy from the curl and the squat in the spinning motion of the flywheel. In the eccentric phase you only do the curl while resisting the flywheel fully and then get an overload eccentric action. In the bottom of the curl, still in a standing position you do a 1 RM curl and then get an easier phase when you go down into the squatting position again.

Progression is Key

What about DOMS then? well, it would be a mistake for a newbie or even an athlete to start doing complete CLAC sessions. Honestly I don’t understand why you would begin with eccentric-only sessions at all. The key is progression. You don’t have to get DOMS to get a positive effect. Start with a set of CLAC in one exercise, say like curl, high pull, military press or bent over row. Add another set in another exercise the next session or within the next week and go on. After a while you can throw in 1-2 sets of CLAC in all exercises in your scheduled workout and get the expected results and be back without long periods of DOMS.

Another option I use myself from time to time when there just isn’t time to workout is finishing off a regular set with 2-3 reps of CLAC in the end. In a compact program just going through 7-8 exercises at 100% intensity for 7-8 reps with CLAC in the end of each set will take you about 4-5 minutes on the kBox and is easy to squeeze in a busy schedule. It’s hard for me to find any more effective 5 minutes spent in a gym that is paying back more. More about this in future posts, promise.

Quick Tips

Finally, some quick tips for eccentric training.

  1. Do eccentric, preferably overloaded actions (ECC+). They are more effective.
  2. Mix it up in your regular training. Don’t do complete sessions of eccentrics.
  3. Start with one ECC+ or CLAC set in one exercise.
  4. Add another 1-2 sets every week in another exercise.
  5. Use kBox for the most dynamic, safest and most sport specific training.

And of course, heavy resistance training requires:

  1. Don’t do heavy training when you don’t feel well or aren’t restituted.
  2. Warm up properly.
  3. Eat well and manage your macronutrients. Make sure you meet your protein need to maximise strength and muscular gains.
  4. Sleep! aim for eight hours a day at least. For adolescent athletes probably even more.
  5. Don’t hold back on the coffee, it attenuates DOMS and the associated decrease in force. (5)

Happy DOMS,

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




References from Twitter


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