4 Weeks to Gorgeous Abs

Your Abs Explained

Transversus Abdominus

The deepest layer of abdominal muscle, it's key to stabilizing your trunk and core. "When you sit for long periods of time, the transversus keeps you from slouching over," says trainer Jeremy Cheung. Strengthen this muscle to help improve your posture.

Rectus Abdominus

Otherwise known as the "six-pack" muscle, its primary function is to bend your spine forward. "Weakness here can cause chronic pelvic instability and lower-back pain," says Cheung.

Obliques

These muscles run on a diagonal up the sides of your midsection, from your pelvis to the bottom of your rib cage. "Life is full of twisting movements, and strengthening your obliques helps support your spine during any type of rotation," explains Cheung.

Iliopsoas

Working these hip-flexor muscles, as well as your lower back and glutes, helps stabilize and support your abs as they work, says Cheung.

Originally published in FITNESS magazine, July 2008.