Shoulder injury

[DickDangleberry]

....and I think this injury has come about incorrectly doing left hooks.

I've had to come out of the habit of using my shoulder and arm to hook rather than stiffing up my arm and using my hip/body to do all the work.

[Bomp]

I'm no physio, but I'd guess the problem comes from technique. It actually sounds similar to a problem I had. There are guys who know more than me on here but I'd guess that you are pushing your punches, i.e. straightening the arm in a press up motion. If you're stance is more side on (or that you twist the body into it) the front muscles aren't engaged as much when you whip out the jab.