Heel-Lifted Squat. Begin with your feet hip-width apart and your left heel lifted. (For an extra challenge, lift the whole foot off the ground and extend your leg in front of you.) With control, push your hips back as you lower your butt toward the floor, bracing your core to help you balance. Don't let your standing knee come out over your toes. Pause, then press into your right heel to stand up into the starting position. That's one rep. Repeat for 45 to 60 seconds before you switch legs.