The serratus anterior

The serratus anterior is a muscle located on the surface of your first 8 ribs, at the side of the chest. When you upwardly rotate and protract the scapula, the serratus stabilizes your shoulder. It’s also often called the boxer’s muscle since boxers heavily use the serratus during punching movements.

To stimulate the serratus, incorporate horizontal and vertical push exercises in which the scapula moves freely [1]. So for instance, with push-ups, avoid having a stiff form with minimal scapular movement. But let your scapula move freely throughout the repetitions.

A full range of motion shoulder press will target the serratus as well. Avoid squeezing the shoulder blades together while pressing. Instead, allow the shoulder blades to rotate upward freely and press the weight all the way up.