I pulled a muscle somewhere in the left side of my chest a couple of weeks ago. At the time, I remarked that you never know just how a muscle is used until it's injured. So here is a brief list of things that are hard or impossible to do with a pulled pectoralis major:
1) breathe deeply
2) run up stairs
4) stand from a sitting position
5) lie on my stomach and watch TV while leaning on my elbows
6) lean on my elbows
8) sneeze (I list this separately because it's a bazillion times more painful than coughing)
I'm sure you can thing of others. As much pain as I was in, it paled to my friend Andrea who, by coincidence, suffered a similar injury. But while mine occurred on a water slide, Andrea's occurred while doing a header on a mountain bike.
I'm such a wuss. These are not, nor have they ever been, my pecs.