This is the subscapularis muscle, it is one of the four muscles that is known as the rotator cuff. When trigger points are developed in this muscle, it may give symptoms of carpal tunnel syndrome. A trained therapist can help you check for trigger points and facilitate healing if you do have any issues with this muscle.
In Strength,
Charles Trinh MS, PES, CSCS, LMT
FunctionWorks Fitness 