Staying healthy should be your main priority. If you are currently injured or something is not feeling right make a doctor visit before training for an ultra. Figure out what is going on before adding more stress and risking further injury that could become more serious. Ask experienced runners within your community who are the expert sports doctors and get a proper evaluation. I prefer Dr. Steven Clouthier at Alternative Health Center of The Woodlands, and Dr. Keith Johnson at Sterling Ridge Orthopaedics & Sports Medicine because both of these doctors are amazing professionals in their field of work and are also endurance athletes. They understand what we athletes go through and are able to relate and help us get healthy again.
There are ways to continue to train that are less demanding on your body if you are dealing with some fatigue or aches and pains. You may want to consider deep water jogging, trying out a zero runner, or running on an Alter-G treadmill. These are great ways to keep up the intensity without abusing your body. You should avoid running if you are limping or you’re changing your gait to decrease the pain. It’s only going to make things worse.