See the section on The Do's and Don'ts of Cross-training for more information. If you must stop running altogether for more than a week, ease back into your running slowly. See Mileage Buildup section for more information. Recognize the difference between fatigue and pain due to an injury. Listen to your body and respect what it is telling you.
Some minor discomforts go away once the muscles warm up.
Be very cautious in this situation as you don't want to cause more serious damage to the injury site. Above all, if pain becomes more intense while running, do not continue . . . walk and begin treatment. If you continue to train and delay treatment, the injury will almost assuredly become more serious, thus jeopardizing the possibility of even being able to participate in the marathon. Consider taking several days off from running along with other types of sports that cause shock to the injured area. Be careful not to take too much of these products as they can cause a variety of internal problems.