Lie on your back and bring your heels together with feet flexed, knees open to the sides. Lift your head and shoulders off the floor and reach both arms by your hips, off the floor.
Press out through your heels and extend your legs straight at a 45-degree angle, squeezing your inner thighs together. Brace your abs in tight, and lower your legs as far down as possible without arching your lower back.
Lift your legs back to your 45-degree angle, and then bend your knees back into your start position (keeping your head lifted the entire time). That’s one rep. Repeat 15 times.