You can find this exercise on page 19 of the book Synergistic Golf.
Exercise Type: BIG BALL
Exercise Category: HIPS, LEGS - FEET, STRENGTH
Lie on your back with arms down by your sides, palms down. Place big ball under feet with legs straight. Pull abdominals in and squeeze your gluteals tight. Lift hips up off the floor while maintaining neutral spine. Try not to allow the ball to move. Focus on strong trunk. For extra challenge, lift one leg to sky and repeat exercise with other leg 10 times.