A body is somersaulting in space, forward or backward.
Anything that makes the body asymmetrical, causes the body to tilt to the left or right.
For example, this guy lifts his left arm, drops his right arm. He tilts as shown in green.
Why? Newton’s 3rd law: For every action, there is an equal and opposite (concurrent) reaction. The body moves in the opposite direction to the arms.
Many gymnasts don’t realize they are tilted. But it’s important to coaches for one BIG reason. The gymnast should un-tilt before coming back to earth. They want to finish the salto symmetrical in most cases.
For example, if the gymnast above wanted to land and stick that twisting skill, he’d move his arms back to where they started. He would un-tilt.
That’s all a coach needs to know about tilt, in my opinion. Too much biomechanical analysis can be worse than not enough. 🙂
If you want to know more, Google Fred Yeadon. One of the top twisting experts. Here’s one of his many articles – Physics World – The physics of twisting somersaults.
The resource I’ve used all my life was written by Hardy Fink.
Technique – An insight into the Biomechanics of Twisting
Gymnastics Coaching.com 