Incorporating stair climbing is a great activity to encourage strengthening of hindlimb muscles. Ensure your dog is taught to perform this exercise slow & controlled – taking each step with each limb individually as opposed to moving quickly or “bunny hopping”.
This can be achieved by either a short lead on a collar or harness, or a “treat” or “lure” held in your hand. You can also set up a “kibble trail” with one piece on each step (be sure to take this out of their allocated food for the day so as to not add extra calories!).