I have a problem... my suplinator longus seems to be rigid and hard on my left arm and has been for years. I am right handed and use a cane with my right hand, so I know that it is not from overuse. The size difference in circumfrance from arm to arm is 1 and a half inches larger on my left arm. I have shown this to my Dr and all he said was "thats interesting" I recently found out, through a physical therapist that I cannot straighten my left arm completely as well and have no idea how long that has been going on. The muscle is hard at all times and bulging but completely painless.