You don't usually get an aerobic workout while on passage offshore, but just the motion of the boat keeps you doing isometric exercises all the time in order to keep from falling or when you are moving around on the boat. Like I said, I always lose weight on passage, and I don't think we've ever missed a meal when offshore even if my wife had to stay by the stove strapped in holding the pots down to keep them from flying off (wish I'd taken a photo of that). Of course, rough weather is generally more exercise, but even easy passages keep you working a lot without even thinking about it. Bracing yourself in to read the charts. Tweaking the sails. Moving about the boat to check things (I always do an evening check of most of the running gear before it gets dark). Etc. I'm not saying that it is like going to the gym every day or running every day, but I seem to always arrive in good shape, though I've never done a passage over two weeks myself. In general I think cruising is an exceptionally healthy lifestyle, which seems to be confirmed by the ripe old ages that many people I know continue to sail at. The things that kill people in our society are driving, smoking, drinking, eating too much unhealthy food, and stress. None of which you need to suffer from when on passage.