You can find this exercise on page 190 of the book Synergistic Golf.
Exercise Type: PILATES
Exercise Category: ABDOMINALS, HIPS, LEGS - FEET, POWER PRODUCTION, STRENGTH
Lie on one side, supporting your head with the lower arm. Your upper arm is in front of your body to help with balance and alignment. Extend both legs along same line as body. Inhale to prepare. Exhale and lift both legs off floor to hip height using muscles on side of hip and waist. Return to floor. Repeat 10x each side.