Thoracic mobility is very important for overhead mobility of the shoulders as well as decreasing stress on the lumbar spine. To assess rotation, perform the lumbar locked internal rotation that will be described below. If one side is limited, rotation to that side is lacking. If both sides are limited, thoracic extension is limited as well.
Begin on knees with toes on the ground. Sit back so that your bottom is on you heels. Place one forearm on the ground and the other hand on the lower back. While maintaining flat forearm, rotate as far towards the up hand as possible. The shoulders should create a 50 degree angle relative to the ground if thoracic rotation isn’t limited.