This exercise combines a Stability Ball with a Medicine Ball.
Steps
Sit on a Stability Ball with your feet firmly on the floor in front of you. Sit with your back straight, your shoulders back and your abs drawn in.
Hold a Medicine Ball in one hand and curl it up bringing your forearm up to your bicep. Return to starting position and switch arms.
Tips
Grasp the Medicine Ball with your fingers spread wide to balance the ball.