Set up: Seated on fitball, feet in front of the ball at hip width apart, core relaxed.
Sitting upright but relaxed, rock your pelvis forward and back by rounding out the lower back (pubic bone towards ribcage) and then reversing this motion by sending tilting the pelvis forward and arching through the lower back. Weight through feet should remain light, and lower limbs relaxed (avoid clenching through thighs and glute muscles).
For circles, rotate hips in a clockwise or counter-clockwise motion as though you are trying to draw a circle with your sit bones. Feel the muscles surrounding your pelvis and lower back release as circles became larger. Focus on slow, smooth movement. Switch to rotate in the opposite direction.