Start standing with your feet hips-width apart. Lean forward and bend both knees, keeping your back flat and your core engaged by pulling it toward your spine. Hold a dumbbell in each hand, palms facing toward each other and arms extended with the dumbbells below your shoulders.
Lift the dumbbells straight up to chest level, bending your elbows and squeezing your shoulder blades together as you do. Be sure to keep your elbows in and pointed upward. Don't arch your back.
Slowly lower the weights back to the starting position. This completes one rep.
Do as many reps as you can in 45 seconds while maintaining proper form.