Alternate arm lifts prone over a stability ball (Core stabilization, lifting arm (alternate), prone over 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.
Keep your feet on the ground.
Slowly lift one arm up in front of you towards your ear.
Lower it back down and repeat with the other arm.