I learned at the CrossFit Gymnastics Seminar that gymnastics is about making shapes. We spend a lot of time at Roots drilling the proper shapes of a kip, so by now you know that the kip consists of 2 shapes; the hollow and the arch. To kip is just to move from one shape to the other efficiently. We kip forward into the arch position and then return to the hollow and pull, and we just did a kipping pull-up. Because the actual pull-up happens in the hollow position many athletes move through the motions of the arch but in anticipation of the pull-up they miss the focus of the arch shape completely and leave a lot of power on the table that could have been applied to the pull-up. In larger sets this becomes more of a problem and when we switch to higher skill movements like the bar muscle-up it becomes a bigger obstacle.
 

So why do we arch to begin with? To be clear, the main picture above is NOT a good arch, though it is a cool picture. When performing the arch we’re trying to create as much tension as possible throughout our body that we will then use as we transition into the hollow to create upward momentum. Our focus in the arch should be creating tension that we can then release through our hollow. The end result is we “pop” upward, our hands become lighter on the bar, sometimes even coming off the bar when we let go. If we were to pull during that moment of “weightlessness” our pull-up becomes much easier, because essentially we weigh less.
 
Tension is created during the arch by keeping the body long and rigid. This is accomplished by keeping the arms and legs straight, the heels squeezed together, butt squeezed and the stomach tight. Some mistaken it for a hyperextended position but when done properly the low-back and hip are locked together and the shoulders and t-spine are doing the work, so mobility their is helpful and can be developed over time. In the beginning this may feel like a much smaller movement than what you’re used to and it may be, but tension isn’t created through size, it is through control and being able to create tight shapes. Remember, gymnastics is about making shapes. Common faults are bending of the legs and/or separation of the feet. When either occur, there is a loss of power. Essentially you’ve taken a long bow and made it a shorter one.
Going back to the basics and getting on the floor to create these shapes is a good start and we do in warmups but if you know this is a struggle of yours throw-in a couple arch-lifts and holds throughout your day. Make sure when you practice you’re not breaking your shape (straight legs, heels squeezed, straight elbows!) so when you hop back on the bar it feels more natural.
Remember, gymnastics is the creation of shapes, so when we’re kipping we’re not just swinging into a position, we should be actively pulling ourselves there. Consider how much work you put into pulling yourself into that shape on the floor and do the same on the bar. Arch to hollow. Hitting the proper hollow shape is also important but for many just correcting the arch shape will show an improvement in pull-ups, muscle-ups, toes-to-bar…