If it's a genuine "pulled" muscle, ie stretched beyond its fright limits, then the one and only surefire method of bringing it back is to keep using it. I'm dead serious. Go swimming, lift weights, work your bullworker, do pressups, play tennis/squash/golf/whatever keeps it moving and working. Ignore initial pain. Forget fatigue. Just keep going, until it comes right, which it will.
Otherwise, keep it iced, and alternate between the physio, the chiropractor, and the acupuncturist.
Then, steadily, get into archery and rowing. You're obviously too old for squash, and these more sedate pursuits will aid your rehab.
And drink more beer. Just because.
