This is a great exercise I've used with runner's who have issues with keeping their hips steading during their runs.
It's an isometric exercise with a large core stabilization component built into it. You're rock solid if you can do this and make it look as if you still have two feet on the floor.
- Lie supine with your feet hip width apart with your knees bent.
- Bridge up squeezing your glutes.
- Now without letting your hips drop, pick one foot up off the floor.
- Put it down and repeat in an alternating fashion for reps.
This is also a great exercise when lightly loaded for individuals seeking more glute hypertrophy.