Part of my training for Tough Mudder has also involved me cutting down on my long distance running which, next to changing my diet has been the most difficult thing for me to do, but its a passion that I can't fight, so I still sneak in runs a couple of days a week...Shhhhh don't tell anyone.
The main reason I am not allowed to run is because we are trying to lower my cortisol levels, and running actually elevates them. Karl King wrote: "If you want to be thin and unhealthy, run lots and lots and lots of slow miles so that your body fills up with cortisol, eating away fat and muscle." That's a scary thought! Do not fret if you are an avid runner because there are ways to run and not raise your cortisol levels to the point of it having negative effects on your body check out this article Are You Losing Muscle Because of Cortisol? .
This article outlines 6 ways to Control Your Cortisol:
1. Keep Your Weight Training Workouts Less Than 1 Hour
2. Limit Your Cardio
6.Limit Caffeine Intake