I have been doing water aerobics for quite a while now. I go to a class two to three times a week in addition to doing other aerobic exercise. It's great for people with joint problems and fibromyalgia--my class has several people with fibromyalgia. If you're doing deep water aerobics, you will use a floatation device so you don't have to worry about being a swimmer at all. According to Fitday, water aerobics burns 3 calories a minute for a person of my weight (I'm assuming Fitday adjusts for weight??).
Edited to answer your other question about what's involved: Most of what you do in water aerobics is what you'd do on land. We "run" through the water, cross country ski, do jumping jacks, etc. We do moves that involve traveling through the water and ones that involve staying in one place. Staying in one place works the core muscles in addition to being aerobic.
I highly recommend water aerobics, especially if you have physical problems. Try it and let us know!
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