Address what kind of injury it is. Ask yourself, can you run without further injury? If yes, then run. Are you telling yourself 'it shouldn't hurt much...' yeah, you're trying to talk yourself into believing a falsehood. Rest. I know it's hard, and frankly I rarely listen to this advice, which makes it so much harder for me to advocate rest. But you are the only one who can decide if it is really worth causing more harm to your body. Rest today, run more later. Run today and get more injured....
Some injuries can be helped by support. I know lots of runners who use KT (kinesiology therapeutic) tape to help support knees, ankles, Achilles, calf strains, hamstring issues, quads, IT bands, sore backs, etc. (Advice from a frequent KT user, if you are male, shave the hair off your knees/legs or use Nair. The tape will stick longer. Clean with rubbing alcohol, spray with Cramer Tuf Skin, then apply KT tape.) There are also ankle and knee braces that you can buy to provide reusable support to your limbs.
|KT tape lasting thru 50 miles!|
|KT tape supporting knees and shins. A little support to S's knee via patellar tendon strap.|
Getting injured during a race is something I rarely think about. This is another judgement call, you have to assess if it is going to cause you additional harm. I've sprained my ankle at mile 7 of a marathon and still finished (because I'm stubborn) and also fallen an scraped myself up at mile 8 of a 50k. The scrape wasn't particularly bothersome if I kept the fabric of my shorts from sticking to it.
I think, in hindsight, that I should have stopped running that particular marathon and saved my ankle.
You've put in all your training and are now in taper mode. BAM.... you get a cold. What now? (As I type this up I am sitting on my couch with a full body ache, cough, and fever. It's really, really fun... especially since I am currently being subjected to Team Umizoomi. Just shoot me now.) I generally run if it is above the chest. A head cold or just headache don't deter me from lacing up. If it is a chest cold or flu, I will reluctantly rest. Bitterly disappointed in what I consider my body's failure to stay healthy. The week before my 50 mile race I was coughing an excessive amount. I had the internal debate of whether or not this was something that might sideline my race. (My son was also coughing more than normal, and of course I took HIM to his doctor. Concerned with some wheezing she heard in his lungs, she prescribed an inhaler and a schedule for treatment. So...... because I already have an inhaler for my exercise induced asthma, I started myself on the same routine. I don't recommend doing this is you don't already have an inhaler prescribed to you!) After about 5 days my coughing was greatly reduced (so was my son's). I really should have taken myself to the doctor, but I really don't like wasting their time with something as trivial as a cough, for me.
Injury and illness happen, it's up to you to know your body well enough to see if you can run through it or if your body needs to rest up. Visit your doctor if you need more information, but my doctor doesn't run.... so I can't believe a word he says about training. Stay healthy and keep running!