Plenty of runners climb on their treadmills or circumvent their neighborhoods every day to build mileage. Some of them will run for good health, some for fun and some because their dogs demand the exercise. But most runners find that racing is where their hard work pays off. You don't have to finish first -- or even 31st -- to feel like a winner when you cross the finish line.
One factor that may attribute to this is runner's high. There comes a point in a long run when everything just clicks: breathing is steady, the stride is even and easy and the body feels just amazing. Runners have referred to this state of euphoria as runner's high. Jesse Pittsley, Ph.D., and president of the American Society for Exercise Physiologists, describes the sensation as "a reduced state of discomfort or pain, and even a loss of time." So is runner's high real? Yes and no. Scientists once thought it came from exercise-released endorphins, but they posit now that it's got more to do with repetition, rhythm and duration [source: WebMD].
An experiment at the Georgia Institute of Technology and University of California, Irvine, found that long-duration exercise produced anadamide, which is a cannabinoid. While the human body makes this molecule naturally, it elicits a feeling not unlike those caused by THC, a chemical found in marijuana. Does the body make itself high? Perhaps. Dr. Arne Dietrich hypothesizes that the body makes these chemicals to counter the sometimes painful effects of exercise [source: CNN].
At the opposite end of the spectrum is the feared phenomenon of hitting the wall. When runners hit the wall -- usually around mile 18 or 20 in the course -- their bodies simply stop functioning. This extreme fatigue can incapacitate runners to different extremes. Some may find that they can limp to the finish line while others have to be carried off the course by medics. So what causes a runner to hit the wall?
It boils down to stored energy: glycogen and fatty acids. Glycogen is your body's biggest source of fuel for running the marathon. Your body tucks it away in the muscles, and when it needs the energy, converts it into glucose -- rapid-release sugar [source: BBC]. The primary reason that marathoners carbo-load (or eat lots of carbohydrates) before the race is to store up glycogen. You can also build glycogen reserves through training. Unlike glycogen, fatty acids are released very slowly. The body stashes them in the tissues and can draw on them in case of emergency. When you're at the wall, this is an emergency -- but your body can't always draw on the reserves fast enough. For those runners you see limping across the finish line, you can assume their bodies have tapped into fatty acid reserves; for those who don't make it, all reserves are likely depleted.
In addition to training (which you can see is preparatory and precautionary), there are other measures you can take while running the marathon to stay sharp and focused. Most importantly, you should hydrate. Most marathons will offer water and electrolyte-infused energy drinks at nearly every mile marker. Others will have food stations on the course with items like bananas that help you rebuild your glycogen stores; some runners will bring energy bars or energy gel packs to replenish their stores.
Listen to your body during the race -- and distinguish between your mind's will to finish and your body's pleas to stop. The thrill of crossing the finish line will be short-lived if you're crippled with pain for weeks afterward. We'll talk more about pain and your health in the next section.