Wednesday Form: "C" what we mean?

Notice the big "C" (on the bottom of the kip). The "abs" and hip flexors lengthen on the front side, and the glutes/lower back squeeze on the backside. That's a very important movement to be able to execute (not just in kipping...but generally). It shows Front/Back muscle balance.

This balanced front/back extension is critical not only in a proper kip as shown, but also in staying tall in squatting, in keeping the bar high/back in a proper push press, sdhp, swing, running, plank...and the list goes on.

Front/back imbalance, tightness due to overtraining one area or weakness due to neglect of an area, is the breeding ground for injury, sorness...ie, sore hip flexors, tight hamstrings, annoying piriformis, etc.
C?