Grip a pair of dumbbells firmly in each hand and stand facing the chair. Bring your right 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 right leg to stand up onto the chair. 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 right knee and driving the hips back, inhaling as you do so. Repeat.