It's Yer Choice or Zen Hand is one of my favorite ways to teach stillness and duration to a dog for fitness behaviors. You are essentially rewarding the dog for not moving towards a treat in your hand.

Here's how I teach this game:

• Grab a treat and put it in a closed fist
• Show the fist to the dog. They will often lick, nibble or paw at the hand trying to get to the treat. Don't give the dog any kind of cue, don't move your hand away from the dog and don't tell the dog no.
• As soon as the dog moves it's mouth or head away from the treat hand, mark that behavior with a click or verbal such as "yes" and give the dog the treat. 
• After the dog will successfully leave the treat hand alone, open the hand with the treat in your palm, palm facing up. If the dog attempts to come get the treat, close your hand into a fist again. Do this as many times as you need to until the dog will not try to take the treat from your open palm. Again there's no verbal cue for this.
• Once the dog will leave the treat alone in your open palm, start extending the amount of time you leave the hand open with the treat sitting on the palm. 

Once you're successful with this game, you can start integrating it into your fitness behaviors and help teach and reward stillness and duration for static exercises.