I’ve had a SUP (stand up paddleboard) for about a year now- it’s a great way to get a core work out. You would not believe the amount of benefit you can get from just paddling around- even in flat water. Every muscle in your body is used to help you balance and control the board and paddle as you propel yourself through the water. And there are many a day (happens quite a bit here in So Fla) where I’ll be the only one out catching a few rides- being that because of the size of the board and and propulsion capabilities of the paddle it is possible to ride waves when even the longboarders cannot catch them (waves that are too small or weak).
It’s catching on in a big way here, and everywhere else from what I’ve seen.
PS- and surfer chicks dig them- works better than a puppy 
