This summer I found swimming very helpful as I have arthritis in both knees. I developed a series of stretching and flexing exercises that really helped tone me up and make me more flexible. I found laps helped develop my breathing and lung capacity. I couldn't do more than 1 lap at a time when I started but would do a lap, some stretching exercises, and another lap. By the time the pool closed I was up to 4 laps twice during my routine! Since the pool closed I've been walking and doing boy flex exercises (modified for my weak knees). Whatever you do, do it consistently and build on it. Swimming laps will work for more of your body than just using a kickboard.