Why it works: Inversions work your core because it takes so much effort to keep your body balanced, but this version of Headstand, where your legs are parallel to the floor, works your core even more. Bound Headstand also tones your upper back.
Get more out of it: Instead of holding your legs in this position, try Headstand Crunches. Slowly lower your feet all the way to the floor, and before touching the ground, slowly raise them up coming into full Headstand. Continue lowering and raising for as many reps as you can, and your abs and upper body will be feeling it in the morning.