Carrie Underwood's Leg Circuit Will Work Every Inch of Your Lower Body

1. Squat down on your right leg, left toes just touching the floor for balance.
2. Without standing up, move your left leg back into a lunge.
3. Keep your right leg bent and return your left leg to starting position.
4. Do 15 reps, then repeat on the other side.

Tip: Don't ever fully stand. The key is to keep the standing leg engaged and burning, says Erin.