Thanks for the replies. Do you guys think it makes a difference that my running is slower and more "steady-state" as opposed to fast sprinting? I figured that since everyone says that steady-state running isn't very effective for fat-loss, it wouldn't really burn much muscle, either. Could I really be burning away my gains by running?
It's not that steady state exercise isn't effective for fat loss. It does. It's that you burn your calories while in that steady state, but when you are done you do not generally continue to burn calories. Or at least not to a great degree. People tote HIIT for the EPOC... Excess Post-exercise Oxygen Consumption. In short terms it boosts your metabolism and keeps it burning even after you are done working out. HIIT is also claimed to be better for type II muscle fibers or fast twitch muscle fibers... which are better for lifting and strength. Steady state plays on Type I or slow twitch muscle fibers.
First, if you enjoy running, keep running. You should enjoy your workouts, sports, etc. I myself run quite a bit to include marathons.
Though the amount of calories burned during your steady state run, coupled with being already worn down before lifting, coupled witht he type I muscle fiber recruitment can all play an adverse effect in your lifting.
I found that the best mix for me is to lift like I want which usually consists of 4 days a week focused on strength programs and then add various forms of HIIT running on top of it. I normally follow Crossfit Endurance's workout of the day for running. Which I try and do either 3 hr before or 3hr after lifting. Occasionally I mix in some longer runs, C2 rower, and such for fun. It's been good for me and I'm happy where I am at, though liek everyone else I'm always trying to get bigger, faster, stronger.