Any time you can push up against gravity, is a good day. If hanging out on your head gives you a headache try this instead. Lie on your back with your knees bent and your feet flat on the floor. Lift your hips up so your body forms a straight line from your shoulders to your knees. Squeeze your THUT and pulse your hips up twenty times, for three reps, or until it's time for the staff meeting. For a challenge, lift one leg up straight to the sky, squeeze and pulse.