Kneel down on the floor with a stability ball in front of you. Place your forearms on the ball, tuck your toes under and extend your legs straight so that you are supporting your body with just your feet and elbows in a plank position. Drive your knees up, tapping the ball while alternating legs. Increase your speed to increase your heart rate. Keep yours shoulders away from your ears. Keep hips in line with your spine.
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