The trick apparently is to push the exercise enough to get the good effect, without overdoing it. Just a little more than you feel like doing . . . . my friend got a (very gentle) horse and enjoys riding very much, she finds that and swimming laps in an indoor pool to be just about right for her.
My daughter would LOVE to have a horse. But we’ll stick with the warm water exercise! I’ve never had any broken bones from warm water! :-)