General Injury Guidelines
Should you run with an injury? Perhaps, so long as you can run at a level of intensity below the threshold of pain without altering your normal running stride. When an injury occurs, at the very least, reduce your mileage and intensity until you can resume running without pain. Do not take medication or ice an injury before testing whether or not you can run without pain, since doing so would only mask the injury and possibly make it worse.
Recognize the difference between fatigue and pain due to an injury. Unfortunately, feel-good endorphins (the chemicals the body produces from aerobic exercise) mask pain. Listen to your body, and respect what it is telling you.
Some minor discomforts go away once muscles warm up. Be very cautious in this case, for you don't want to cause more serious damage to an injury site. Above all, if pain becomes more intense while running, do not continue. Stop and walk and then begin treating the injury when you get home.
If something hurts, do not run; instead, choose a cross-training activity to maintain cardiovascular fitness. The following sports are generally safe for injured runners but check with your doctor for clearance: walking, elliptical training, cycling, swimming, deep-water running, rowing, yoga, and Pilates. If you must stop running altogether for more than a week, ease back into your running slowly.