The Clydesdale, in marathons, is a category of male runner. Like its namesake horse, Clydesdale runners are large and sturdy, built for power more than for speed -- unlike your typically lean marathoner. Runners in this category race with all the other runners but compete within the category to provide them with fair competition -- so a runner may finish poorly overall, but still win his category. For larger marathoners, the category offers an opportunity to participate competitively in a marathon.
Weight
The Clydesdale marathon category is a weight category for men. Runner's in this category must weigh above a certain amount. This weight varies depending on the race organizers, but according to "Runner's World," the cutoff is usually between 200 and 220 pounds. A similar category, called the Athena category, exists for women with a cutoff of between 145 and 160 pounds.
Purpose
The Clydesdale weight category serves a purpose similar to age and gender categories -- to allow competitors to compete with others who are at a similar running level. Jeffrey West, a 245-pound marathoner, told the "New York Times," "As a Clydesdale, you know you’re never going to win a race." But these larger competitors can compete against each other. This gives larger runners a competitive incentive in the race.
History
The Clydesdale category emerged in the 1980s after a Baltimore accountant analyzed runners in 10-kilometer and marathon races. He found that after men reached 170 pounds, their performance declined relative to their weight. This meant that a large, slower runner might actually be performing better than a smaller, faster runner. As a result, some smaller races began offering the Clydesdale category. Eventually the category was adopted by larger races such as the Marine Corps Marathon and the Portland Marathon.
Training
According to professional runner Lauren Fleshman, Clydesdale marathoners need to take special precautions to avoid injury. She recommends building up weekly mileage by 5 to 10 percent. She also advises Clydesdale runners to learn proper running techniques. Because they are applying so much more weight to their joints than the average runner, a Clydesdale marathoner is much more likely to injure himself with improper form.