The kneeling stability-ball curl and extension combination requires good balance on the ball.

Muscle group: Biceps

Steps

Hold dumbbells with an underhand grip. Kneel on the ball with abs braced and back neutral. Raise one arm above your shoulder while the other remains curled. Bend the raised arm behind your head as in a triceps extension; at the same time, lower the other weight and curl it back up. Return and exchange the arms' roles.

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