I did about an hour of interval training yesterday and still felt fairly fresh. I decided to do a little upper body workout. I typically do cardio and strength training on separate days. After cooling down a little and decided to do several sets of pull-ups and dips. As I jumped up to grab the pull-up bar, I felt a huge tug in my chest. That's never happened before. About an hour later, it stiffened up and continued to get worse through the night. I pretty sure I pulled a muscle in my chest. Is it better to stretchi out the muscle or refrain from straining it when possible?