I've been given this exercise in physical therapy a few different times as it's a great multipurpose exercise for practicing balance and strengthening the muscles around the hip. Plus it's pretty fun and you can join the circus once you get really good at it. It's a great thing to do pre- surgery to strengthen and also post -surgery if you have muscle atrophy (wasting or loss) from the surgery and recovery. Always check with your physical therapist first, of course! You do need a small exercise trampoline for this but to get stated you can always just do it on solid ground. The trampoline just adds to the balancing element of the excercise. As you can see in the video, I wobble a lot, especially on my left leg. This weakness, we think, is from those crazy six months on crutches after my last surgery. To do this stand on one leg and have someone throw you a ball. At first they can throw it straight at you but as you get used to it they should begin to throw it to the left, right and higher or lower. This forces you to move your body to catch the ball which in turn tests your balance. Depending on your tolerance you can switch legs every 30 to 60 seconds but you should stop if you have pain.