The serratus anterior is that cool-looking muscle on the side of the upper abs area, sometimes referred to as the "boxer's muscle." It isn't technically an abdominal muscle, but it completes the look of a muscular, shredded torso.

Arnold

Problem is, it's kinda tough to train directly. In fact, many strength coaches say to forget about targeting the serratus and instead just get your body fat very low and do lots of overhead presses and pullovers, which bring the serratus into play. Not bad advice, but you can directly target this muscle group. Here's how:

Serratus Cable Crunch

  1. Stand sideways to a high cable with a D-handle. If your left side is facing the handle, reach up with your left hand and grab it.
  2. Place your right hand on the left serratus. This is a form of touch training and will help you target and contract the serratus.
  3. Bend in the opposite direction to get a full stretch, then "crunch" the serratus down and forward slightly. Hold the crunched position for a few seconds for full effect.
  4. After 6 to 12 reps, switch and train the other side.

This one takes some practice. Adjust your position until you can feel the serratus contract. Once you develop that mind-muscle connection, it'll be easier.

Related:  4 Minutes to Core Strength

Related:  The Four Dumbest Ab Exercises