I found some very interesting information at Kevin Sayers' web site here.
Thank you to the following for their comments about weight training for ultra runners: Kevin Sayers, Karl King, Charles Steele.
The benefits of weight lifting to running ultras are the same as the benefits of weight lifting to any other endurance activity.
Think on this statement for a minute: "A chain is only as strong as its weakest link."
You see, when we run, we use more muscles than just our legs. We use our entire body. The body, during exercise, acts as a kinetic chain, whereby energy is transferred from the upper body and into the lower body - thus giving us propulsion. When the upper body is weak, the energy transfer is not as efficient, and our performance suffers. Makes sense?
If not, try this: The next time you run, run with your hands in your pants pockets. This inhibits the transfer of energy from the upper body, making running a lot more difficult. Sound silly? Where are your arms near the end of a 50-miler? (For me, the answer is simple: They usually end up closer to my pants pockets than they should be!)
How does upper body exercise increase running efficiency? It increases the efficiency by which the body utilizes energy - by more easily transferring the stored, potential energy into kinetic energy that is used for forward motion. So upper body strength is important to running well - I just wish I had the stamina to work on my arm strength as much as I work on my leg strength. After an event, are your shoulders just as tired as your legs? I know that mine are!
Karl King#1
For those who are beginners at lifting, beware the terrible Ts: too much, too fast, too soon. Think of your program as very long term - there's no need to rush. I've talked with many runners who tried weights, got injured and gave up on them.
When you first start, progress is very rapid. But, it takes eight weeks of work before you get any significant muscle adaptation. The early, rapid improvements are almost all neurological: your brain becomes more adept at telling your muscle fibers how to contract to lift the load. Beginners get excited at their rapid progress and increase the load far too fast. Then they get injured because they're over stressing the muscle fibers and probably connective tissue as well.
Start slow, and use high reps-low weights for a couple months to give your body a chance to
