There's a lot of breathing in choir. That may seem like an obvious statement, so I'll move on quickly. It turns out, that if you get sick during a mid-semester break, after you have been consistently exercising your diaphragm (through almost 3 hours a week of singing), that the muscles you then strain while coughing are muscles that you use for darn well everything. Standing up straight, for example, and biking. And walking, and balancing in heels. And a different facet of breathing.
The little random stabs of agony have almost gone away, and I can stand up straight again, and walk again at my normal clip, and I have managed not to acquire an ibuprofen habit while getting to this point. I have to laugh though--choir, in addition to its multifarious advantages (like getting to sing for almost 3 hours a week :-D), has given me new and more interesting ways to hurt myself.
Once my intercostals, or whatever muscles I managed to strain, are fully healed again, you can bet that part of my regimen will be strengthening them so I don't go through this again. Ow.