Running

Running is defined as the fastest means for an animal to move 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. It can be a form of both aerobic and anaerobic exercise.

Human running mechanics
Running is a complex, coordinated process that involves the entire body. Every human being runs differently, but certain general features of running motion are common.

Lower body motion
Running 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.

Support
During the support phase, the foot is in contact with the ground and supports the body against gravity. The body's center of mass is typically somewhere in the lower abdominal area between the hips. The supporting foot touches ground slightly ahead of the point that lies directly below the body's center 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. To what extent it flexes varies with the running style. There exist stiff-legged running styles which reduce knee flexion, and looser, or more dynamic running styles which 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 ilio-tibial band of the supporting leg, the hip abductor, and the abdominals and lower back muscles. The knee flexion is opposed by the eccentric contraction of the quadriceps muscle. The supporting hip continues to extend and the body's center 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 hip, 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 running style, is aimed squarely at the runner's center 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 running 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 running styles, additional power comes from the calves as they extend the foot for a longer drive. This motion is most exhibited in sprinting.

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 rapidly stretch. 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.

Upper body motion
The motions of the upper body are essential to maintaining balance and a forward motion for optimal running. They compensate for the motions of the lower body, keeping the body in rotational balance. A leg's recovery is matched by a forward drive of the opposite arm, and a leg's support and drive motions are balanced by backward movement of the opposite arm. The shoulders and torso are also involved. Because the leg drive is slower than the kick of recovery, the arm thrusting backward is slower also. The downward arm drive is more forceful and rapid.

The more force exerted by the lower body, the more exaggerated do the upper body motions have to be to absorb the momentum. While it is possible to run without movements of the arms, the spine and shoulders will generally still be recruited. Using the arms to absorb the forces aids in maintaining balance at higher speed. Otherwise, optimal force would be hard to attain for fear of falling over.

Most of the energy expended in running goes to the compensating motions, and so considerable gains in running speed as well as economy can be made by eliminating wasteful or incorrect motions.

For instance, if the force vector in the drive phase is aimed too far away from the center of mass of the body, it will transfer an angular momentum to the body which has to be absorbed. If a free body in space is struck off-center by a projectile, it will rotate as well as recoil. If the projectile strikes the body's center of mass exactly, the object will recoil only, without rotating.

The faster the running, the more energy has to be dissipated through compensating motions throughout the entire body. This is why elite sprinters have powerful upper body physiques. As the competitive distance increases, there is a rapid drop in the upper body and overall muscle mass typically exhibited by the people who compete at a high level in each respective event.

Upright posture and a slight forward lean
Leaning forward places a runner's center of mass on the front part of the foot, which avoids landing on the heel and facilitates the use of the spring mechanism of the foot. It also makes it easier for the runner to avoid landing the foot in front of the center of mass and the resultant braking effect.

Stride rate
Exercise physiologists have found that the stride rates are extremely consistent across professional runners, between 185 and 200 steps per minute. The main difference between long- and short-distance runners is the length of stride rather than the rate of stride.

During running, the speed at which the runner moves may be calculated by multiplying the cadence (steps per second) by the stride length. Running is often measured in terms of pace or minutes per mile or kilometer.

Using smooth circular leg motion
Many people have compared the motion of the legs and feet when running to pendulums. This is incorrect. A pendulum has a natural frequency of motion. For a human leg, this is usually much slower than the frequency of leg motion when running. When one uses a pendulum leg motion for running at a frequency higher than one's legs' natural frequency, the energy expenditure to simply maintain that motion will grow exponentially with respect to frequency. This is very inefficient. Intuitively, this amounts to swinging the leg forward, using muscular power to stop the forward swing of the leg and accelerate it backward, using muscular power to stop the backward swing of the leg and accelerate it forward, ... and so on.

In comparison to a pendulum motion, a circular motion is one that preserves the angular momentum of an object revolving around a center. An object moving in a circular orbit will not require any additional energy for continued motion in the absence of friction regardless of the frequency. When running efficiently, the foot motion approximates a smooth circle, capturing as much of the rotational kinetic energy of the foot as possible.

An anecdotal example of a good circular running form is that adopted by the typical competitive Kenyan runner. To an observer, Kenyans' running form seem to have a very exaggerated motion with high lift of the heel. Many people would postulate that lifting the heels that high would require a lot of muscular power from the hamstring and thus be inefficient. In reality, most of the heel lift is accomplished by the preservation of angular momentum of the feet without the use of muscular power. The high heel lift is an integral part of preserving the circular motion and efficiently preserving the rotation kinetic energy of the feet.

Running versus Walking
Running can burn approximately 200 percent more calories per hour than walking.

In walking, 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; in comparison, humans actually jump from one leg to the other while running. Each jump 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 of the ground. This continual rise and fall of bodyweight expends a tremendous amount of energy opposing gravity and absorbing shock during take-off and landing. . The act of running involves using more energy to accomplish travel over the same distance and running is a less efficient means of locomotion in terms of calories expended, though it is more efficient in terms of distance traveled per unit time.

Running injuries
Due to its high-impact nature, there are many injuries associated with running. Common injuries include "runner's knee" (pain in the knee), shin splints, pulled muscles (especially the hamstring), "jogger's nipple" (irritation of the nipple due to friction), twisted ankles, iliotibial band syndrome, plantar fasciitis, and Achilles tendinitis. Stress fractures are also fairly common in runners training at a high volume or intensity. The most common running-related injuries are due to over-exertion or bad running form. Repetitive stress on the same tissues without enough time for recovery or running with improper form can lead to many of the above. Generally these injuries can be minimized by warming up beforehand, wearing proper running shoes, improving running form, performing strength training exercises, and getting enough rest. There is a strong consensus among the running and scientific community that all of those can be effective in both minimizing and recovering from running injuries.

Another injury prevention method common in the running community is stretching. Stretching is often recommended as a requirement to avoid running injuries, and it is almost uniformly performed by competitive runners of any level. Recent medical literature, however, finds mixed effects of stretching prior to running. One study found insufficient evidence to support the claim that stretching prior to running was effective in injury prevention or soreness reduction,. Another, however, has demonstrated that stretching prior to running increases injuries, while stretching afterwards actually decreases them.

Inconsistent experimental methodology and the failure to use proper stretching methods are reasons given to explain the conflicting results. Because of this, members of the running community argue that stretching remains helpful.

Jogging
Jogging is a vaguely-defined term which generally refers to a type of slow running, which may have originated in the UK. Previously called "roadwork" in the US when athletes in training, such as boxers, customarily ran several miles each day as part of their conditioning, In the 1960s to 1970s the word "roadwork" was mostly supplanted by the word "jogging," as the activity gained popularity.

Running as a sport
Running is both a competitive sport and a type of training for sports which have running or endurance components. As a sport it is split into events divided by distance and sometimes includes permutations such as the obstacles in Steeplechase. Perhaps the most basic of athletic contests, running races are simply contests to determine which of the competitors is able to run a certain distance in the shortest time. Today, competitive running events make up the core of the sport of athletics. Events are usually grouped into several classes, each requiring substantially different athletic strengths and involving different tactics, training methods, and types of competitors.

Running competitions have probably existed for most of humanity's history, and were a key part of the ancient Olympic Games as well as the modern Olympics.

Types of running events

 * Track running
 * Road running
 * Cross country running
 * Trail running
 * Fell running
 * Relay Race

Classification of running by distance

 * Sprints
 * Middle distance
 * Long distance
 * Marathon
 * Ultrarunning
 * Multiday running