those little trampolines can be helpful.....With PN I would consider one ONLY if it has the sort of 'handle' and only after proper training with a PT. I've used one under supervision, but the balance issues for getting on and off were IFFY! For those who are fit...[I remember waay back then] they can be useful. I prefer a pair of balance discs myself, they take up less room and can give your legs, feet and ankles a workout -provided you have something to hold onto! - j

PS The balance discs are a bit more low-impact than what I think you're looking for. Water exercise classes mite be an option...when they make you 'dash' water-walking from one end of a pool to another...well, you DO know your cardio is WORKING!?