What could be wrong if my left shoulder pain when working out?

Shoulders complicatd: There can be many reasons for this - a muscle strain or joint sprain, a slightly torn tendon, and irritated bursa, an unstable shoulder joint, arthritis, torn cartilage, or shoulder parts jamming each other on motion. This requires a careful shoulder examination by a rehab or orthopedic doc. Don't let this go on too long. James dillard, md.