Serratus anterior can be found when you place your hand at the bottom of your armpit and move it downard a bit - gentle self-massage here can feel wonderful. The muscle begins on the back of your body, and continues across the side and onto the front/side edge of your body. It is an important muscle for many reasons, and is used in breathing and lifting an am overhead.
Rigidity/restriction in the area of serratus anterior has many unpleasant repercussions, both in the area and through the entire body.
Working on this area can produce sensations of tenderness, but does not have to be painful.
The benefits of having work done here are many: increasing ease and range of motion - including in breath - and proper balance and inter-relationship between bony structures, locally and through the body.