Running

This article is about locomotion in humans. For running in horses, see Horse gait. For locomotion in dogs, see Gait (dog). For general locomotion, see Gait. For other uses, see Running (disambiguation).

Edward Muybridge photo sequence
People running at the 2007 Brussels marathonRunning is a means of terrestrial locomotion allowing a human or an animal to move rapidly on foot. It is simply defined in athletics terms as a gait in which at regular points during the running cycle both feet are off the ground. This is in contrast to walking, where one foot is always in contact with the ground, the legs are kept mostly straight and the center of gravity vaults over the legs in an inverted pendulum fashion.[1] A characteristic feature of a running body from the viewpoint of spring-mass mechanics, is that changes in kinetic and potential energy within a stride occur simultaneously, with energy storage accomplished by springy tendons and passive muscle elasticity.[2]The term running can refer to any of a variety of speeds ranging from jogging to sprinting.

The ancestors of mankind developed the ability to run about four and a half million years ago, probably in order to hunt animals. Competitive running grew out of religious festivals in various areas. Records of competitive racing date back to the Tailteann Games in Ireland in 1829 BCE, while the first recorded Olympic Games took place in 776 BCE.
Humans leap from one leg to the other while running. Each leap raises the center of gravity during take-off and lowers it on landing as the knee bends to absorb the shock. At mid arc, both feet are momentarily off the ground. This continual rise and fall of bodyweight expends energy opposing gravity and absorbing shock during take-off and landing. Running on a track requires more energy than walking to cover the same distance due to air resistance at higher speeds. However on a treadmill running and walking require the same amount of energy to cover the same distance.[citation needed] As reported by Hall et al. males on a track running at a pace of 6.3 mph use 1.20 times as much energy to travel the same distance as walking at a pace of 3.15 mph, but on a treadmill running 6.3 mph uses just 1.01 times as much energy to travel the same distance as walking at 3.15 mph.[7] Therefore, running is less efficient than walking in terms of calories expended per unit distance, though it is faster.

Running is executed as a sequence of strides, which alternate between the two legs. Each leg's stride can be roughly divided into three phases: support, drive, and recovery. Support and drive occur when the foot is in contact with the ground. Recovery occurs when the foot is off the ground. Since only one foot is on the ground at a time in running, one leg is always in recovery, while the other goes through support and drive. Then, briefly, as the runner leaps through the air, both legs are in recovery. These phases are described in detail below.