This move shapes up the hamstrings and lifts that hard-to-reach spot where the glutes and hamstrings meet.
How to do it: Lie face down on the floor, bend your elbows and stack your hands under your forehead. Extend both legs straight out behind you, pointing your toes and squeezing your heels together [A]. Press your shoulders down and lift both legs slightly off the floor. Keeping your feet touching, bend your knees (knees can open out to the sides slightly as they bend) and curl both heels in towards your body [B]. Without letting your knees touch the ground, slowly extend both legs back out straight. Repeat 15 times total (Try doing another set of 15 before finishing the workout if you can).
Quick Form Tip: Be sure to keep your kneecaps lifted off the floor during the full movement, and imagine you are pressing your heels into something as you bend your knees in, to really squeeze the backs of your thighs.