A great exercise for anyone who wants to strengthen your abs and train to keep the balance. It involves the whole body and for its implementation does not require any special equipment. All you need - a small towel and a slippery floor;)
I've always admired the way some yoga teachers do a headstand or hands. They do not repel your feet off the floor. Not. They do it gently and gracefully. As if their body does not depend on gravity and other laws of the earth. It is subject only to its owner. They rest against your hands and slowly pulled up to his feet first and then pretty easy to pick up the straightened leg. Of course, the ability to keep the balance standing there in the first place, but believe me, raise your legs straight with the help of only one media - not an easy task. To do this for a long time to train.
If you are a beginner, you perform the exercises, pulling your knees to your chest. If it's too easy for you, complicates the task and tightens straight legs to the body, a smooth transition from plank pose in "dog upside down" or, as it is called, "the hill."
By the way, at the primary level are taught to first lift straight legs to stand on his head, and then go to the bar on his hands.