The long run is an essential training tool for marathoners. Your body must learn to spare glycogen (it's stored fuel), metabolize fat as fuel, and develop the strength and endurance necessary to complete the 26.2 miles in one piece.
The long run also allows you to develop the psychological fortitude needed to hang in there on race day. But every marathoner is a unique combination of a multitude of variables that influence training. The long run can take a different form for each runner. Your goal is to optimize training benefits without suffering injury, since added miles increase risk.
What Do Elite Runners Do?
Elite marathoners typically take regular long training runs of 20 to 23 miles; some even cover 30 miles on occasion. A 22-mile training run demands 2 1/2 hours for an elite female and less for an elite male. Consider that a runner takes about 90 steps with each leg per minute of running or 13,000 steps with each leg during a typical long run.
Impact and training time contribute to overuse injury, along with a greater chance of dehydration and heat or cold stress. A recreational runner (for example a 4:45 marathoner) must accommodate twice the amount of impact or 26,000 steps with each leg and twice the training time and stress as the elite marathoner.
Don't worry that you won't be able to complete a 4:30 marathon if you have never run beyond two and a half hours in training. In fact, it is not necessary to train at such a high percentage of your race distance no matter what the course.
If you run a steady two miles every day for two months, you would be able to complete a 10K. You wouldn't need to take regular 80-mile runs for a 100-miler, nor do you need to run 20 miles to prepare for a marathon.
Running too long will set the stage for over-training injuries before race day even arrives. It may be better, over the long haul, to run the same training time for your long run as the elite runner, rather than the same mileage.
Consider the Walk/Run Approach
If your goal is to complete a marathon and to feel reasonably good doing it, consider a walk/run approach and use it from the start of your long training runs and the race itself, not after you're starting to suffer.
You may complete a marathon in less time alternately running and walking the whole way than you can by trying to run non-stop. If you try a walk/run method, practice different walk/run ratios during your long training sessions to find the best one for you.
The Psychological Factor
Understand that on the all-important day of the marathon, things will be quite different from typical training days. After planning for months, you will be rested and trained. You will be highly motivated and among hordes of spectators and other runners who will be cheering you on.
The first hour of the run will fly by and before you know it you will be half way, not even realizing that you have just surpassed the distance of most of your long training runs. Don't focus on how far you've gone or have yet to go. Just concentrate on the task at hand and all will go well.
Run relaxed and confident, take your fluids regularly, and focus on your stride rate and breathing now and then. Go over the things that you have learned and remember why you are out there. The thrill of the day and the groundwork you've done will carry you through your ultimate long run.