When I was first married, I still cared about being "buff." I played softball, so having strong abdominal, leg, back, chest, and arm muscles was beneficial for hitting and running.
In retrospect, the hours in the gym maybe led to six home runs and a fairly questionable status of being "buff." Those hours may have been better spent taking a nap after my 5:00 a.m to 2:00 p.m. shift at a Mayo Clinic lab.
To those who enjoy lifting weights, more power to you. As a runner, I can appreciate the goal setting involved--reaching a new maximum lift on the bench press; squatting twice your body weight for the first time; setting up a program to build a strength base on which to increase your maximum power--all of these are very similar to a running program.
For runners who weight train, the biggest piece of advice I can give is this: you are an experiment of one. If you like lifting heavy weights and enjoy the muscle tone you see in the mirror, keep lifting how you're lifting.
If you like being a little bulkier to achieve that Men's Health cover model look, go right ahead with your heavy weights and moderate repetitions.
If, however, you want to lift to prevent injury and/or become a faster runner, you may want to consider changing your lifting routine. More mass = more weight to carry over any given distance. If that mass is lean muscle of the slow twitch or intermediate fast twitch variety, you may see performance improvements (read about muscle fibers here).
Again, you are an experiment of one, and there are many factors that aid or hinder performance other than weight or body composition. In the end, more mass equals more weight to carry and more load on your joints. Look at the body types of elite runners, and on the whole you'll see lean women and men with very little mass in their shoulders, arms, or pectoral muscles.
If you want to know what the ideal body type looks like for marathon runners, watch this video:
I'm bias toward body weight exercises: running specific yoga and core training, calf raises on my stairs, and glute exercises to reduce the likelihood of overuse injuries.
Thanks to the miracle of the internet, finding running-related workouts is easier than ever. Runner's World has a "Yoga Center" where you can watch yoga routines specifically for runners.
While these videos are helpful, finding an in-person yoga instructor who can help with your own body peculiarities can be even more beneficial. My long rib cage is great for lung capacity, but on certain yoga poses it presses against my long, narrow hips, making some twisting poses uncomfortable.
A couple of years ago, I was doing yoga with an excellent instructor at the YMCA. She knew that runners do not want a lot of static flexibility in the hamstrings, and she consistently offered alternative poses or rolled-up blankets to make poses more comfortable.
After a few sessions with her, I'm now more comfortable doing yoga on my own. Unfortunately, the instructor moved to California, though I can't say that I blame her. At the last session I attended she was several minutes late because her car wouldn't start--the air temperature that morning was negative five degrees F.
The biggest difficulty I have with strength training is sticking to a routine. If I have an extra hour, I want to run. What's been most helpful for me is doing short routines of ten to twenty minutes. There's no need to set aside an hour when less time will suffice to prevent injury.
Look for future posts on cross training for runners. Strength training can be fun, but I much prefer cycling or hiking to hanging out in a gym.