Running and lower body workouts

runnersconnenect.net is of my favorite running resources because the information they share is based on peer reviewed studies not on hype, fad or personal opinion. The site sells training plans and other resources but they also have a good blog with a lot of interesting and informative articles. Here's one that discusses stabilization and strength training for masters runners.

http://runnersconnect.net/masters-running/strength-masters-runners/

In general, everything I have read indicates as we age strength training becomes more and more critical for overall body maintenance and injury prevention, so regardless of any competition-specific goals, keeping going with some form of your weight training appears to be a very good idea. My own personal experience is when I am maintaining a consistent strength training regimen I feel a lot stronger running especially on hills and my form tends not to break down as much when I start feeling fatigued.

I run 3-4 days each week. During race season I run half marathons but in the summer I stick to 5Ks because it's just too hot to run long distances. My training runs right now are 5K on weekdays and a 10K on the weekend, early in the morning before the heat sets in. I do upper body strength training and only add legs one day each week. I do find that my legs feel more fatigued the day or two after legs.

I mentioned the half marathons because this past Fall and Winter I found that I needed to stop the lower body workouts the last few weeks before a race. At that point, every run was at least 6 miles and it was really hard to start out with legs that were already tired. I could probably have still done it, and it might even have led to being stronger and faster in the end, but mentally it was really tough.

All of that said, I started weight lifting last Spring but I've been running since 2011. This past year I've made the biggest gains in speed and stamina. I attribute a lot of that to the lifting. If nothing else, my legs sure do look nicer.

So... lift weights, including legs, on a regular basis but you may want to skip legs the week or two before a 5K race so they're not fatigued for the big days.

Everyone will disagree with me, but I consider running hills to be strength training

You've gotten great advice. I can't really add to it other than to say I really get the desire to lighten lower body ST during running season. I do lower body once a week and try to do it the day before a rest day. I generally walk on RDs, so it stretches out the muscles nicely before picking up running again the following day.

Honestly, you can't beat a plyometric workout though. So give up a ST day once in a while for plyo.

Running, no matter what the incline, is not strength training. If you strap on a bunch of weights, it might be a good ab/core exercise, but the range of motion in the leg musculature is nowhere near being large enough for any meaningful strength training.