Why it's on the list: No, we're not going to echo that old myth that squats and deads are all you need for abs. You need more! But there's no debating that both front and back squats force you to learn how to brace your abs to maintain a neutral, upright position. And before you say, "It doesn't count if you wear a lifting belt," a number of studies have shown that a belt actually increases ab activation during squats.
Oh, and don't worry about balancing on a BOSU ball to increase the work of your stabilizers. Research has shown that if you just go heavy with your squats on the floor, you'll get all the ab stimulus you need.
Squat Variations for Ab Development:
In your workout: Regularly program both back and front squats into your routine. To keep it interesting, rotate through in four-week waves, or alternate weeks between back and fronts. Also, if you're following a dedicated program like the 7-Day Six-Pack, do your workouts after your heavy leg days, not before. The last thing you want is to feel sore or weak when you're under the bar!