Rick David Online PT - "Floor Bridges" follow along 1:00 w/detailed description.

Here's how to do Floor Bridges:
Begin by lying on your back with bent knees and feet at hip width, arms straight and down by your sides with thumbs turned up and the back of your head comfortably resting on the floor. With your belly button drawn in to activate your core, flex your hamstrings and glutes to raise your hips remembering to keep your core activated without arching your back. This will give your hips a posterior tilt resulting in a lower back and hip flexor stretch. Driving with your heels as opposed to your toes will isolate your hamstrings and glutes to keep the correct muscles activated for this exercise.