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Running is a means of terrestrial locomotion allowing a human or an animal to move rapidly on foot. It is defined in sporting terms as a gait in which at some point all feet are off the ground at the same time. 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 rides along fairly smoothly on top of the legs. The term can refer to any of a variety of speeds ranging from jogging to sprinting. According to legend the first competitive race in ancient Greece took place in the year 776 BCE on Mount Olympus.
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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. Jogging uses more energy than walking to travel the same distance. Therefore, running is less efficient than walking in terms of calories expended per unit distance, though it is faster. In 2004, scientists at the University of Utah and Harvard University hypothesized that the ability of humans to sustain a long-distance endurance run may have been instrumental in the evolution of the human form.
Lower body motion
While 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 each step, 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.
Support
During the support phase, the foot is in contact with the ground and supports the body against gravity. The body's centre of mass is typically somewhere in the lower abdominal area between the hips. The supporting foot touches the ground slightly ahead of the point that lies directly below the body's centre of mass. The knee joint is at its greatest extension just prior to the support phase. When contact is made with the ground, the knee joint begins to flex, and the extent it flexes varies with
style. Stiff-legged styles reduce knee flexion, and looser, or more dynamic, styles increase it. As the supporting leg bends at the knee, the pelvis dips down on the opposite side. These motions absorb shock and are opposed by the coordinated action of several muscles. The pelvic dip is opposed by the tensor fasciae lataeilio-tibial band of the supporting leg, the hip abductor, and the abdominals and lower back muscles. The knee flexion is opposed by the Muscle contraction[clarification needed] eccentric contraction of the quadriceps muscle. The supporting hip continues to extend, and the body's centre of mass passes over the supporting leg. The knee then begins to extend, and the opposite hip rises from its brief dip. The support phase begins to transition into drive.
Drive
The support phase quickly transitions into the drive phase. The drive leg extends at the knee joint, and at the hips, such that the toe maintains contact with the ground as that leg trails behind the body. The foot pushes backward and also down, creating a diagonal force vector, which, in an efficient style, is aimed squarely at the runner's centre of mass. Since the diagonal vector has a vertical component, the drive phase continues to provide some support against gravity and can be regarded as an extension of the support phase. During the drive, the foot may extend also, by a flexing of the soleus and gastrocnemius muscle in the calf. In some styles, notably long-distance "shuffles" which keep the feet close to the ground, the ankle remains more or less rigid during drive. Because the knee joint straightens, though not completely, much of the power of the drive comes from the quadriceps muscle group, and in some styles, additional power comes from the calves as they extend the foot for a longer drive. This motion is most exhibited in sprinting. There has been much discussion about the exact nature of the drive phase, because it has now been shown scientifically that the quadriceps have no activity after the supporting phase; this has become known as the extensor paradox. Essentially our body automatically turns off the quadriceps after the bodyweight moves forward of its supporting foot. This has led to a hypothesis that there is no driving phase , and that the runner's own bodyweight is providing the propulsion during this time essentially falling through a gravitational torque created as the general centres of mass of the runner is in a forward position from the supporting foot.
Recovery
When the driving toe loses contact with the ground, the recovery phase begins. During recovery, the hip flexes, which rapidly drives the knee forward. Much of the motion of the lower leg is driven by the forces transferred from the upper leg rather than by the action of the muscles. As the knee kicks forward, it exerts torque against the lower leg through the knee joint, causing the leg to snap upward. The degree of leg lift can be consciously adjusted by the runner, with additional muscle power. During the last stage of recovery, the hip achieves maximal flexion, and, as the lower leg rapidly unfolds, which it does in a passive way, the knee joint also reaches its greatest, though not full, extension. During this extension of the leg and flexion of the hip, the hamstring and gluteal muscles are required to stretch rapidly. Muscles which are stretched respond by contracting by a reflex action. Recovery ends when the foot comes into contact with the ground, transitioning again into the support phase.