About The kBox4 and Eccentric Training

Introducing the kBox4, my newest toy for my personal training clients.

The kBox4 is a flywheel trainer that uses inertia to create resistance rather than weights and gravity. The main aspect of the kBox4 is that you have to work for the entire duration of the rep and set, it uses the kinetic energy that you use to lift to lower you back down. The harder you lift the more inertia you create, so you can pull slowly and light or fast and heavy and with that force it will pull you back down with the exact amount of force.

When training, your muscles are much stronger in the eccentric (lengthening) phase of contraction compared to the concentric (shortening) phase. An easy example would be you can jump down from a 4ft wall but you can't jump up a 4ft wall. The concentric helps develop the "software" such as increased motor unit recruitment and the eccentric helps develop the "hardware" such as increased cross sectional area and number of muscle fibres. (This is a very basic example, much more happens but we don't need to go into it!)

Eccentric training has strong scientific support, the most important being increasing total strength and hypertrophy (building muscle). Many injuries occur during eccentric contraction because the muscle is lengthening under load being more susceptible to tears. Eccentric training can greatly reduce the risk of injury for elite athletes as well as provide faster recovery for rehabilitation clients. Eccentric training has also been shown to transform muscle into a faster phenotype (type 1 slow twitch to type 2 fast twitch) this meaning increases in the muscles power and speed.

Exxentric kBox4
Exxentric kBox4

Training with the kBox4

In regular weight training the load in the eccentric phase is limited to how much the weaker concentric phase can lift, because of this the eccentric phase is never loaded to its maximum unless you have assistance, as such the training loses efficiency. The first thing I noticed when I used the kBox4 was how early in a set I fatigued! Typically, in a set of 10 you fatigue around rep 7 if the load is correct, the weight will be consistently submaximal until you fatigue, with the kBox4 the weight is variable because it's based on each individual rep so you reach fatigue much quicker if you put the effort in.

I have my kBox4 fitted with the kMeter which is a strain gauge that measures rep by rep power output so I can see exactly how much force you are producing on each rep. Very cool! It also means I can see how hard you're working so there's no chance of slacking off!

Exxentric Kmeter
Exxentric Kmeter

As I mentioned earlier the kBox4 makes you work for the entire set because you have no time to rest at the top of the rep. This is because with each exercise you set the belt length to full range of motion or its longest point away (squats would be standing fully extended) and as soon as the belt reaches full length the axle attached to the flywheel collects the belt again and pulls you straight back down.

Benefits of the kBox4

The main point / benefit of the kBox4 over regular weight training is having to control to eccentric phase. I've mentioned the benefits of training the eccentric phase but how often do you see people just drop the weights or lower faster than they lift? This is majorly reducing the effectiveness of their training because they're not utilising the eccentric phase, with the kBox4 you HAVE to control this phase of the exercise otherwise things won't end well!

Training with the kBox4 also gives you the opportunity to uniquely overload the eccentric phase in comparison to the concentric. This is where the party really starts! A great example of this would be your typical bad form bicep curl that you see in the gym... you know, the guy stood in front of the dumbbell rack hip thrusting up a 30kg dumbbell! Well, you can slightly fine tune this by using your hips and legs to assist the concentric phase and then be super strict with the arms on the eccentric phase, allowing you to generate more inertia to elicit higher peak eccentric force gaining better results. This isn't just limited to arms; you can use the arms to assist in overloading the legs in exercises like squats.

The kBox4 has been a major asset to my training not having to lug around different weights, it's one piece of equipment that I can deliver a functional, full body workout with as much load as the trainee can manage. It's also been great for my group training sessions because there's no changing weights on or off bars, just the effort each individual puts into the exercise, it makes it safer as technique doesn't falter as fatigue sets in because its set by only the force that you can put into it and the kBox4 help reduce any insecurities as no one can tell what you're lifting so there's no ego lifting!

If this looks good to you and you're local to East Sussex, then get in touch to book some sessions.