On the court the other day, I had a tennis player immediately complain of trying to serve really hard and feeling immediate pain in the center of the right side of her back thereafter. She could no longer lift her arm above 90 degrees and do any overhead motion including serves and reaching for a higher ball.
The Pec Minor was primarily powering her serve forward and thus her surrounding musculature including her lower and mid trapezius were not participating at all. 
The Pec Minor’s main action is to draw the scapula forward and downward. Considering most activities in our day to day life require movement in front, this particular muscle can over power and take charge in many activities including sitting at a desk, throwing activities and serving.
For this particular player, she needs to release her pec minor and strengthen her lower and mid trapezius.
One of my favorite exercises for strengthening the lower trapezius and the posterior chain of the body is the TRX Overhead Squat and the TRX T Fly for the middle trapezius.
TRX Overhead Squat TRX T Fly
If you are having trouble in movement, get assessed! Pain is your body telling you to get checked out.
http://locomotiontherapy.com/movement-therapy/schedule-an-therapy-session/