Running and strength training do not mix. When I say "strength training" I am referring to the typical bodybulding workouts to failure that grace most of the muscle magazines every month. The issue is overtraining. Serious strength training requires that the body have prolonged periods of rest to recover, and mixing various runs with today's "latest" multi-set split routines puts tremendous fatigue on the body.
Plus, body building routines and training for a marathon have distinctly different goals. Most elite runners are lean -- very lean. They have just enough muscle tissue in order to accomplish the demands that a marathon places on the body. Physiologically, someone training for a marathon is training to body's skeletal system for endurance. A body builder is trying to get bigger. Hypertrophy, the "pumping up" of muscle and sorrounding fiber, is the goal. A traditional body building routine sacrifices endurance deliberately for muscle size and plumpness.
Being totally and completely new to running I can hardly call myself an expert. But in looking through the raft of books on long distance running at the local Border's and Barnes & Noble (not to mention the ability to look at scanned in pages on amazon.com) I've noticed some serious issues with how most running books approach recommending a strength training routine. Every book I've seen has placed the emphasis on machine style circuit training.
There are a number of problems with this approach. Without debating the value of machines versus using free weights too much, it is easy to look at this from a functional perspective. Machines produce isolation movements and work a specific muscle. Machine based weight training looks at the body as a sum of piece parts by and large. Large compound movements like the squat and deadlift engage all of the muscles in the body. They are "functional" in that your whole body has to coordinate the movement and it's strength response in order to suceed. Building up total muscle skeleton endurance is easier using large compound movements.
Circuit training routines typically combine many exercises one right after another with little rest between exercises. The idea is to get some of the benefits of strength training and cardiovascular training all rolled into one. The problem is specificity. There are specific proteins, amino acids, and biochemical responses to trigger in order to gain strength. There are specific proteins, amino acids, and biochemical responses to trigger in order to increase indurance. There is no set of proteins, amino acids, or biochemical responses to trigger that can do both.
The benefit of strength training for a runner should be more dense muscular fiber -- dense, not bigger -- and an anaeorbic ability to "sprint" for short bursts under increased work load. Also, strength training can be used to improve musclar skeleton issues like a weak lower back, weak knees, poor abdominal strength, etc. All of these can benefit a runner. So what is needed an approach that doesn't overtrain the body and still provides functional benefit and an increased density of muscle.
Instead of 4 sets to compete failure, or 10-12 exercises of 8-12 repetitions with little no rest in between a more balanced (and some would say "old school" power lifting approach) is ideal. 3-5 exercises. 3-5 sets per exercise. 3-5 minutes of rest between sets. The 3-5 exercises should focus on large compound movements like squats, deadlifts, bench presses, dips, pull ups, pull overs, clean and jerks, and shoulder presses. Never train to failure. When you finish a set of 5 repetitions you feel like you could have done 1-2 more reps.
Focusing on large compounds movements provides muscular stress and development to the entire body. 3-5 minutes of rest per set allows the body time to recover and rest up. Not training to failure prevents overtraining. Start a "3x5" routine like this with weights for each exercise that you could easily do 10 repetitions of. Plan on working out 3 times a week. Add 5-10 pounds per exercise per workout -- or not if you feel like you couldn't complete the 3-5 reps at that poundage. Do this for 4-6 weeks and then cycle back to the beginning -- this time with a starting weight that is a little higher than last time's starting weight. And change the order of the exercises (you don't have to change the exercises themselves).
This type of strength training routine was the standard approach for building a strong, hard body up until the steriod crazed body building era began. This mixes well with running and any other endurance sport because it is focused, brief, intense, and does not completely tax the body. What it develops is the central nervous system's ability to respond to load and stress. And that can come in handy when you need that extra kick on that last 400 yards.
