Footspeed, or sprint speed, is the maximum speed at which a human can run. It is affected by many factors, varies greatly throughout the population, and is important in athletics and many sports, such as association football, rugby, and American football.
Factors in speed 
The key determinant of footspeed in sprinting is the predominance of one distinct type of muscle fibre over another, specifically the ratio of fast-twitch muscles to slow-twitch muscles in a sprinter's physical makeup. Though fast-twitch muscles produce no more energy than slow-twitch muscles when they contract, they do so more rapidly through a process of anaerobic metabolism, though at the cost of inferior efficiency over longer periods of firing. The average human has an almost-equal ratio of fast-twitch to slow-twitch fibers, but top sprinters may have as much as 80% fast-twitch fibers, while top long-distance runners may have only 20%. This ratio is believed to have genetic origins, though some assert that it can be adjusted by muscle training.[Dead link] "Speed camps" and "Speed Training Manuals", which purport to provide fractional increases in maximum footspeed, are popular among budding professional athletes, and some sources estimate that 17% to 19% of speed can be trained.[Dead link]
Though good running form is useful in increasing speed, fast and slow runners have been shown to move their legs at nearly the same rate – it is the force exerted by the leg on the ground that separates fast sprinters from slow. Top short-distance runners exert as much as four times their body weight in pressure on the running surface. For this reason, muscle mass in the legs, relative to total body weight, is a key factor in maximizing footspeed.
Limits of speed 
The fastest human footspeed on record is 44.72 km/h (27.79 mph), seen during a 100 metres sprint (average speed between the 60th and the 80th meter) by Usain Bolt. Maximum human sprint speed is strikingly slower than that of many animals. Compared to other land animals, humans are exceptionally capable of endurance, but exceptionally incapable of great speed. For example, cheetahs can attain short bursts of speed well over 100 km/h (62 mph), the American quarter horse has topped 88 km/h (55 mph), greyhounds can reach 70 km/h (43 mph), and the Mongolian Wild Ass has been measured at 64 km/h (40 mph). Even the domestic cat may reach 48 km/h (30 mph). Some people incorrectly believe that all these animals would lose in a long distance race with a human.[verification needed] An example would be the Man versus Horse Marathon, where horses with saddle and rider have bested almost all runners often by more than 25%.
The primary advantage humans have over most land animals is a superior method of cooling themselves. Most land animals cool themselves by panting, while humans are able to shed heat via perspiration. On a hot day, similar to the African climate where humans evolved, many land animals would overheat and fatigue much faster than humans. In Wales, where the Man versus Horse Marathon is held, the highest average temperature for any month is only 22 °C (72 °F). The lower temperature reduces the cooling advantage humans possess. Indeed, in the years that humans have won the Man versus Horse Marathon, the weather was reported as hot.
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