Did you miss a run last week due to a morning meeting? Have to take a few days off when you caught the flu? Don't stress about it, McDowell says.
"It's super easy to become really anal about getting in every training run, but if you're sick or work gets in the way occasionally, don't sweat missing a couple runs. It is much better to get to the starting line slightly under trained than overtrained—or sick or injured."
Just make sure to get right back to your training plan as soon as you feel better and your schedule is back on track.