This is a very simple and crucial question. And understanding it makes dancing so much more straightforward.
Marks tend to yank or hurl on their limbs in order to create rotation, destabilizing themselves.
Rotation around our own spine is controlled by the obliques, shaded light blue in the image at right.
Muscles work most strongly when their insertion points are stable. That means that if you yank your shoulder or hurl your free leg in an attempt to create strength in your turn you are actually undermining the work of the only muscles that can actually do it.
Keep your body stable, using hip flexion. Then use the oblique muscles to rotate your body around the spine.
Use this technique to mark ochos and giros and to revel ocho, voleo-circular, and all pivots.
