Glycogen is your body's most readily available form of fuel, but, fortunately for long-distance runners, it's not their only fuel. Your body can also convert fat into energy, and even the slimmest of runners store enough body fat to cover approximately 600 miles -- the equivalent of nearly 29 marathons! The problem is, fat requires oxygen to burn, and if you're running at a good clip, you are said to be running anaerobically, which means "in the absence of oxygen." [source: Medical Dictionary] Anaerobic running also increases the amount of waste products in your blood, leading to a burning sensation in the muscles. [source: Galloway] So, what's an aspiring marathoner who wants to run her fastest possible race to do?
Former world-record-holding marathoner Juma Ikangaa once said, "The will to win means nothing without the will to prepare." [source: Will-Weber] Show up at a race fueled by Hollywood hype and inadequate training, and you're asking for trouble. You'll run anaerobically, exhaust your body's glycogen reserves and discover that your day has followed a humiliating script that no director would think of putting on the silver screen, save as a comedy.
But with consistent running over a period of weeks and months, you'll become winded less-easily. Your anaerobic threshold -- the point at which your body draws its energy from non-oxygenated sources like glucose -- will be pushed back. You'll be able to run farther and faster and burn a mixture of glycogen and fat.
Be advised, however, that even the fittest of athletes can make the mistake of letting their adrenaline dictate an unrealistic pace. Race day emotions, not to mention cheering crowds and competition, can cause a regional champion to think he can run with the international stars. If that pace is considerably faster than he encountered in training, he will likely come face to face with a large, brick structure that only he sees at mile 20 -- if not before.
Proper nutrition prior to and during the race is also key. An adequate, though not overindulgent, pre-race breakfast high in carbohydrates is ideal because carbs can be burned aerobically or anaerobically. Energy gels and drinks, which are also high in carbohydrates, can be taken approximately every 45 minutes during the marathon to top off your energy stores and stave off depletion longer. You'll want to experiment in training with what agrees with your stomach -- some runners find that particular mixtures create nausea and even vomiting.