Metrication in the United States traditional mile-based lengths. In the Olympics, athletes run 1500 meters, not 1600 meters. Running races in the U.S. are usually run in metric distances (e.g., the 100 metres dash or the 5K run), although the mile distance remains popular. But even 5 and 10 kilometer races most often have mile markers on the course, and no kilometer markers. Long-distance races are often measured in kilometers, although exceptions exist (generally 10 mile races). The marathon is referred to as a 26.219-mile race (the official marathon standard distance originally being in English units — 26 miles, 385 yards) rather than 42.195 km.
Marathon swimming Marathon swimming Marathon swimming is a class of open water swimming defined by long distances (at least 10 kilometers) and traditional rules based in English Channel swimming. Unlike marathon foot-races which have a specifically defined distance, "marathon swims" vary in distance. However, one commonly used minimum definition is 10 kilometers, the distance of the marathon swimming event at the Olympic Games. As in all open water swimming, tides, surface currents and wind-chop are major determinants of finish-times. For a given course, these factors can vary dramatically from day to day, making any attempt to draw conclusions about athletic ability by