Position a box a couple feet to the side of a bench. Hold a dumbbell to your chest with both hands and seat yourself on the bench facing the box. This will be your starting position. Plant your feet firmly on the ground as you lean forward, extending through the hips and knees to jump up and forward. Land on the box with both feet, absorbing the impact by allowing the hips and knees to bend. Step down and return to the starting position.