Start standing with your feet slightly wider than hip-width apart. Hold one dumbbell in both hands and engage your core by pulling it in toward your spine.
Looking straight ahead, bend at the hips and knees until your thighs are parallel to the floor and your elbows tap your knees. Make sure your knees don't go past your toes, and keep your core pulled in toward your spine and your chest lifted.
Drive through your heels to return to standing.
This counts as one rep. Complete as many reps as you can with proper form in 20 seconds.