Grip a single dumbbell firmly in your right hand and stand facing the bench. Move your arm so you are holding the dumbbell directly overhead with your elbow locked out. Bring your left knee up and step up on to the bench. Brace your core and keep your chest up as you drive all your weight through your left leg to stand up onto the bench. All the while exhaling as you do so. Pause at top when it's fully extended. Slowly return to the start position by bending at the left knee and driving the hips back, inhaling as you do so. Repeat all the required reps (or time) on one side before changing to the other.