What is This Cord Like Tendon/muscle Under my Arm? What Shall I Do? (photo)

OK So about 2 to 3 years ago, i was training for cross fit games, i guess i wasn't properly warmed up at the time, and i needed to do muscle ups, a pull up into a dip on a pull up bar, and first rep in i struggled due to tight shoulders and one shoulder rotated over the bar and the other one didn't, my weight pushed me down, and i believe i tore my bicep and pectoral. i was 230lbs 6'2. After the bruising went away, i have a string like cord under my arm and but no pain, just tight. what is this?