How to: Lay flat on your back with both feet flat on the floor, draw-in your navel & extend through your hips until knee, hip & shoulders are aligned. Then draw 1 knee into the chest without dropping or rotating the hips. Hold for 1-3 sec.
Compensations: Watch for dropping of the hips, even the slightest. The goals is to show no movement. Watch for elevation of the shoulders to help brace.