Tip: A New Way to Build Core Strength

The two dozen muscles between your hips and shoulders do more than flex and stabilize. So to really hit your "core" you'll need to do more than just crunches. Try this.

Lying Leg Raise with Stabilization

Tie a band around the bottom of the squat rack, preferably the knobs of the pins. If you don't have a squat rack, secure the ends of the bands to some dumbbells. Just make sure you have enough tension to get the main benefits. Get your chest under the band, press up, and hold.
Lock down your shoulders, rib cage, and more importantly, the entire backside of the posterior chain because the instability of the band might cause you to slide if you're not dialed in correctly.
Lift at your legs and make sure the movement occurs at the hips, not in your lower back. If you're sliding back and forth, your rib cage is flaring. Reset and try them again.
Oh, and don't forget to breathe.

How It Works

The regular hanging leg raise works all the muscles of the midsection, hip flexors, lats, and grip. However, if you don't have adequate strength, endurance, or flexibility, your spine starts to curve and low back pain sets in, which is an issue. This exercise fixes those problems.

The resistance band creates tension and instability in the locked-out position.
All the muscles in the entire body must be engaged throughout the movement, encouraging you to keep your core tight throughout.
The band increases the demand on the upper body while your ability to maintain a tight neutral spine is challenged when lowering the legs.