What lat muscle did I pull?

The latissimus dorsi is the largest and most used back muscle, according to MyWeightLifting.com, so it's the most likely to be injured when working the upper back. Pain more toward the center of the back may be in the trapezius. MedLinePlus recommends icing and compression for strained muscles and ligaments.

The rotator cuff, which is located directly above the lats, can also be injured when performing back exercises, according to BodyBuilding.com. The rhomboids and teres major muscles work with the rotator cuff when squeezing shoulders together and in rotation movements, as shown on MyWeighLlifting.com. The injured muscle depends on the specific area where the pain is centered.