Both the half marathon and marathon distances are popular for runners of all ability levels. While there is often a progression from running 5Ks and 10Ks to a half marathon before graduating to the marathon distance, sometimes new runners want to jump right to the marathon.
But there is an important physiological challenge to running the marathon that the shorter distances lack. Simply put, your body does not have enough stored glycogen—the body's preferred energy source when running—to finish a marathon. There's a flip side: The body has plenty of stored glycogen to finish a half marathon.
You're probably thinking, "Great. But what does knowing that little factoid have to do with training for a half marathon or training for a marathon?"
Long, Long Runs for Marathon Preparation
What we find at the the world-class level down to the amateur level is that many runners can run a solid half-marathon time, but fail to run the equivalent marathon time. For example, if you can run a half marathon in 1:55, then you should be able to run a marathon in about 4 hours.
But to reach your goal in the marathon, you'll have to be able to burn some fat (also called lipid metabolism). This is where many runners fail—they've done enough work to run a good half marathon (i.e. threshold runs, longs runs, some workouts at race pace, as well as some workouts at 5K and 10K pace)—but they've failed to do the serious long runs (sometimes called "long, long runs"), or the training runs that last as long as they hope to race.
Yes, that's right, you should consider building up your long run to the same duration that you hope to race. Now, if you're shooting for 4 hours, then that's 9:10 pace. I'm not saying you have to run 9:10 per mile for 26.2 miles on a training run. But, what if you ran 10-minute miles and then walked for a minute or two every 3 to 4 miles? You would cover roughly 22 miles in 4 hours. That type of workout is a great way to teach your body to utilize fat during the marathon.
Half Marathon Versus Marathon Training
Obviously this isn't the only key for running a solid marathon, but it is the big difference between sound marathon training plans and half marathon training plans. Good half marathon training plans don't require you to run a workout focused on fat metabolism, whereas sound marathon training will have at least one or two long, long runs that put you in a state where your body has to utilize fat.
More: Fat as Fuel?
There are other differences between half marathon training plans and marathon training plans: the importance of solid 5K and 10K PRs as a predictor of half-marathon success, and the importance a slow progression of long runs for marathon success. Yet it's the role of fat metabolism that is the biggest difference between the two types of training plans. If you understand that difference and then use that knowledge to influence your training, then you can run to your potential at the marathon distance.marathon or half marathon.