Great question
There are two areas that can shut a person down. One is the physiological wall and the other is more mental. Of these, the physiological wall is the true wall.
The wall is the point where ones body simply shuts down and says NO MORE due to glycogen (sugar) depletion. In real simple terms, the body runs on fat and sugar during the run and the body can only store about 90 minutes of sugar for use on the run. The shut down occurs because the brain can only burn sugar as its fuel; therefore, once stores hit a certain level, the brain goes into self-preservation mode. You can prevent this from occurring by being properly hydrated and fueled before and during the race AND running in an aerobic mode commiserate with your level of training. Head out too fast, come into the day improperly nourished and you too can hit the miserable wall.
What most of us hit is the mental area where we let the brain convince the body to back off. Like the wall, it generally occurs somewhere after a couple hours of activity (though it can occur at mile 2 or never occur). For many, it occurs 2-3 miles past the longest training run. Generally, we are doing great well into a marathon and then a tweak is felt, hit an unexpected hill, a potty break is perceived
we stop, slow then have a tough time restarting.
A great example is a marathon runner running continuously through about mile 17. For what ever reason he stops for a short walk and then from there he is simply unable to string a complete mile together for the 3-4 miles of the race.
Another example is the runner who trained to a 21 mile long run and at mile 24 feels like he can go no further.
A final example is a run/walker who also include aid stations as walks. Somewhere around mile 16 they end a walk segment and look up to see the next aid station and simply walk into and through the station; basically doubling or so the walk break. The longer than normal walk sets the wheels in motion so the runner becomes a walker for the next 5 miles.
These mental breaks are all too common. I have suffered many of them actually, all of them as these are from some of my 20+ marathons. You will see me talk of the mental toolbox that we develop through the training season. These are the little tricks and gimmicks we find that help get us through a tough training run. Simply try to log your feelings and thoughts during your long runs. By going back over a long run and thinking of the positive things that occurred you are building the toolbox up for race day.
Toolbox items can and will include things like a special go to song on the iPhone, trying to pace off of a runner 20 feet or so in front of you by tying an imaginary rubber band around the front runner, having a special gel (food) in you pack for that trouble spot, forcing yourself to run to the next landmark, streetlight or crack in the road, if caught in a walk, picking a spot to start a run from. There is also the mile-by-mile dedication to those who have influenced you
or possibly to those who tried to tell you how dumb your marathon adventure was.
Often a few seconds of swim motion of the arms to kill stress along with a couple deep cleansing breaths are enough to snap you out of a mid race funk. I find that I run my better miles when I can clear my mind and simply run in a zone. I once hit that zone in the TTC area and then ran through the MK and almost to DAK before I realized where I was. It was my best Disney marathon, but it did take a couple days before I could recall the events in the MK area.
Generally these mental obstacles will prevent the physiological wall from occurring. Remember, the marathon is really 90% mental if you run well hydrated and fueled and run within a pace supported by your training.
Hope this helps
