You don't have to be paddling on a SUP to work the THUT. Stand wherever you are, hip-width apart. Pull your navel back to your spine. Slide one leg straight behind you. Lift that foot a few inches off of the floor. You can do this in front of your desk, in the kitchen, (eating over your sink) or on the subway platform. Squeeze the THUT and pulse the leg up 20 reps, or until you're fatigued, or your car arrives. Switch legs.