According to the National Council on Strength and Fitness, the average human can run at the speed of 15 miles per hour for short periods of time. This speed varies greatly depending on factors such as age, weight, culture, wind and even height of the individual.
The key determinant of a human speed limit is biological. It is heavily influenced by the predominance of fast-twitch muscles over slow-twitch muscles that make up a sprinter's physics. The first type produces more energy through anaerobic metabolism, which is essential in attaining higher speeds within a short time period. On the other hand, the slow-twitch muscle produces same amount of energy through aerobic respiration but does not influence an increase in speed. As of 2014, the fastest foot speed on record is 27.44 miles per hour set by Usain Bolt.