One of the most important factors in marathon training is tempo running, which is defined as + 10 seconds per mile from your projected marathon pace. If you’re planning on running 26.2 miles at 7:00 per mile, then do lots of training at or near this pace.
This is one of the major differences between elite runners’ marathon training and others training for the event.
Most runners or joggers are simply trying to finish the event in halfway decent condition. Elite runners are essentially “racing” the event. That is, they will attempt to run 26.2 miles at a pace faster than their everyday run pace. Nearly everyone else is running marathons slower than their everyday pace. Marathon race pace for elite runners is at an interesting point, physiologically speaking. Many terms are used to describe this level, such as “threshold” and “capacity.” They all describe the same thing.
Marathon pace usually uses most of the capacity of the aerobic energy system and very little of the anaerobic energy systems. Traditional road race and track training tends to ignore this marathon pace. Most training is done well above or below it. But the marathon is a unique event, and one of the limiting factors to performance is fuel economy, and training at projected marathon tempo trains your body to use fuel (specificallycarbohydrate) efficiently.
Tempo runs are used to prepare your body to run at your desired marathon speed. They are longish intervals conducted at marathon pace and generally done on a hard surface. Recovery between each tempo period should be an easy jog.