This deep lunge and balance combo will help tighten the backs of your thighs in no time.
How to do it: Start standing with your feet together. Take a big step forward with your right leg. Reaching towards your right foot with both hands and hinging slightly forward from your hips, bend both knees into a low lunge (be sure to keep your right knee lined up over your right ankle at the bottom of your lunge. Don't let your knee extend past your toes). Your left knee should be pointed straight down to the floor (like a sprinter about to start running) [A].
Next, press your weight into your right leg and push down through your right foot as you stand up out of the lunge, lifting your left leg off the floor and straight up behind your hip. Your upper body should maintain the hinged forward position as you stand, with your back straight, abs tight [B]. Balance for one count and then lower back down into the lunge. If it's too hard to stand on one leg, try tapping your left foot lightly on the floor behind you as you stand up out of the lunge. Repeat 15 times and then switch to the other side.
Quick Form Tip: As you stand out of the lunge position, focus on one point on the floor in front of you. This will help you balance at the top of the move.