Get up and go to the pencil sharpener, if possible. Step outside during your lunch break or walk to get a drink of water. If you want to get in shape but you’re too busy to hit the gym, you need to at least get yourself up and active. Walk. Park on the far side of the parking area.
If you must sit at school and/or work, then move your legs and body about, but not constantly like a pendulum.
Write something about yourself. No need to be fancy, just an overview.