Funny to revisit this thread ... curious to know if the physical demands have lessened for y'all? I agree with BroVan above...kook stage was intense. It still is intense in too-light wind, when frantically pumping, I am shocked how gassed I get ... add in dodging big surf and that can be hyperventilating 200bpm feeling-like-i-might-faint better-work-on-cardio level.
But other than that...when properly powered and with a harness, it can sometimes be so easy that it doesn't feel like exercise. I find I can regularly go an hour with falling in, hair still dry halfway through session ... and sometimes find I get a little chilly from not moving enough. It is like the early kiting days, all us middle agers were bragging about having abs again, from the intensity of fun and engaging exercise. Then we started kite foiling and got fat again.