Find a sturdy bench, coffee table, wooden box, or kid's chair that allows your knee to be at about a 90-degree angle or larger when you place your foot squarely on it.
Hold a dumbbell in each hand by your side.
Step your right foot onto the box, then your left, so both feet are on top of the box.
Softly step the right foot back to the ground, then the left.
This counts as one rep.
Keep alternating step-ups for 40 seconds, followed by a 20-second rest.