I used to run 45 miles per week and was a competitive 5K and half marathon runner.
for me it hindered me greatly.
it was the extra water weight, extra muscle, and the shin and calf pumps.
there is a guy who posted a thread who said he ran a very low dose of var and dbol i believe and he said it helped him. so its a very iffy situation, if you find the perfect dosage i suppose you can pull it off
you cannot be great at both, you have to choose either bodybuilding or endurance running. all that extra muscle is gonna weigh you down. heck as a triathlete I noticed when is started putting on muscle I started sinking like a rock when I would swim.