Opposite arm and leg lift prone over a stability ball

Kneel on the floor with a stability ball in front of you.
Roll forwards over the ball until you are lying on it with the ball under your hips.
Place your hands on the floor under your shoulders.
Ensure your feet are on the ground.
Slowly lift one arm up in front of you and the opposite leg out behind you.
Do not arch your back.
Lower back down and repeat with the other arm and leg.