To begin this exercise place your front foot on a step while balancing on the ball of your rear foot as demonstrated.
Lower yourself into a deep lunge position by bending your back knee. Try to keep a parallel alignment between your trunk and front shin bone. To avoid straining your hips, only drop down as far as comfortable. Return to the start position, by pushing up through the heel of your front foot.
Your physiotherapist will advise whether you should perform this exercise with any weights.