Bridge semi on stability ball ("Bridge" Core/gluteals strengthening, focus on control, feet on stability ball)

Lie on your back with your legs on a stability ball.
Flatten the curve of your lower back against the floor by tucking your tail bone underneath you.
Gently pull in your pelvic floor.
Tighten your buttock muscles and lift up your hips so that your pelvis comes off the floor.
The focus is on the control of the movement and not how far you can lift up your hips.
Make sure you breathe evenly, and hold the ball steady throughout.