I am a 50 yr old male who just got back into playing tennis competitively. I am currently a 3.5 on the improve. I need to increase my fitness and cardio. I get winded quickly and that translates into sloppy footwork and we all know what that translates to So whats a good way to improve my cardio in a way that I can start gradually and build up as I go? I don't want to spend thousands on home machines and dont want to pay a monthly fee to a gym. So what's left? -skipping rope? -bicycling? (I have a hybrid and a mountain bike) -running or jogging? -cardio tennis classes? -spinning classes? My problem is I get winded on tough points or long rallies and play MUCH better when not out of breath.