Clamshell By strengthening your outer hips and glutes with this move, you're providing more support to your hips and lower back, Speir says. Lie on your side with your head resting in your hand. Stack your legs in a 90-degree bend. Raise your top knee to open the thighs like butterfly wings — your heels should be touching as you maintain the bend in your legs. Open and close the top knee while only using your leg muscles to drive the movement — keep the hips still. Repeat 20 times.