This evening I worked up to 545lbs for 2 solid reps, the only problem was on my underhand grip side; my lat (very high armpit area to a little down my tricep)seemed to get strained pretty bad, it almost felt like my muscle released/elongated during the lift. I still have pretty good pain in it, I was able to finish the workout except it was rather painful to fully extend on pull ups & pull downs. Has anyone else encountered this, what are your thoughts?
My thought would be you strained your lat or rotator cuff that was working to keep your arm in its socket. RICE.
as stated above...you probably have a subscapularis strain. Be a little careful on the pulldown motions (ie. chins) and ice, ice, ice.
A little ART can go a long way also. You definately don't want that to become a chronic injury.