Training outdoors is an excellent way to prepare, especially since you'll be running outside on race day. But if you live in an urban area, you may be dealing with poor air quality during your runs.
"Try to run early in the morning before all of the car pollution gets going, and avoid running on the road when possible. Instead, look for a local park or trail system," Clayton says.
If you just can't handle outdoor runs or the weather won't allow it, try altering your incline during your treadmill session to help mimic the uneven terrain you'll be covering on race day.
