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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 is a form of both anaerobic exercise and aerobic exercise.
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.
Human running mechanics
Running is a complex, coordinated process which involves the entire body. Every human being runs differently, but certain general features of running motion are common.
Lower body motion
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.
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 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.
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.
When 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 into the support phase.
Upper body motion
The motions of the upper body are essential in running, because they compensate for the motions of the lower body, keeping the body in rotational balance. A leg's recovery is matched by a downward drive of the opposite arm, and a leg's support and drive motions are balanced by raising of the opposite arm. The shoulders and torso are also involved. Because the leg drive is slower than the kick of recovery, the arm raising motion is slower also. The downward arm drive is more forceful and rapid.
The more inefficient the motions of the lower body, the more exaggerated do the upper body motions have to be to absorb the momentum.
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.
Overrunning can cause broken bones, lack of calcium, spine aches, back aches, legs aches, and stomach pain.
Elements of good running technique
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.
Most elite runners in the world run at a stride rate of 180 strides per minute regardless of the running distance and the runner's physical build. It has been postulated that human physiology dictates that the 180 stride rate is the most efficent in terms of energy expenditure when running. Most beginning runners have a lower stride rate. This may cause most of the energy to be expended in vertical movement rather than in overcoming the friction of air. Also, low stride rate may also be indicative of overstriding.
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 exagerated 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.
There are many injuries associated with running (due to it being a high impact activity). Common injuries are "runner's knee" (pain in the knee), shin splints, pulled muscles (especially the hamstring), "jogger's nipple" (soreness of the nipple due to friction), twisted ankles, Iliotibial Band Syndrome, Plantar fasciitis, and achilles tendonitis. 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-use or, more often, bad running form. Repetitive stress on the same tissues without enough time for recovery or due to improper form or muscle imbalances, leads to many of the above. Generally these can be minimized by warming up beforehand, wearing proper running shoes, improving running form, performing strengthening exercises, and getting enough rest. There is a very strong consensus among the running and scientific community that all of those can be very effective in minimizing or recovering from running injuries.
Another injury prevention method that is very commonly recommended in the running community, but has recently become controversial, is stretching. While stretching is often recommended as a near requirement to avoid running injuries and is almost uniformly performed by competitive runners of any level, medical literature shows only mixed results, in particular for stretching prior to running.
A 2002 survey of 27 peer reviewed studies found that there was not sufficient evidence to support the claim that stretching prior to running was effective in injury prevention or soreness reduction.
Nonetheless, other studies have shown that stretching after training consistently reduces injuries. 
Most members of the running community find that the inconsistent study methods and the failure to establish proper controls and find proper stretching methods is the reason behind the conflicting studies. They argue that, therefore, stretching is in fact helpful, or at least not harmful.
Jogging is a vaguely-defined term which generally refers to a type of slow running, previously called "roadwork" 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" and this form of running became quite popular among many people at that time, mainly throughout the Western world.
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 fastest. Today, competitive running events make up the core of the sport of athletics.
Running competitions have probably existed for most of humanity's history, and were a key part of the ancient Greek Olympics, as well as the modern Olympic games.
Events are usually grouped into several classes, each requiring substantially different athletic strengths and involving different tactics, training methods, and types of competitors.
Running affects not only the body, but the mind as well. Runners who finish a great run are sometimes said to have a runner's high — which is more than a sensation of a strong feeling of accomplishment and pride. Some sources point to the origin of a runner's high being increased endorphin production as a result of exercise. However, many runners also do not experience this high.
Running in itself makes up its own competitive sport, but running is also a very important aspect of other sports, i.e. association football, rugby, basketball, lacrosse,etc. Usually the running aspect of these sports is very important to help move a ball to a goal. People of all running types are needed; i.e. with speed, endurance, or agility.
Types of running events
- Track running
- Road running
- Cross-country running
- Trail running
- Fell running
Classification of running by distance
- Middle distance
- Long distance
- Multiday running
- Sports Injury Information: Running
- Athletics Weekly website
- Runner's World website
- Running advice for beginners
- SearchRunning.com - Search engine for runners website
- Running Encyclopedia website
- Big London Charity Race every summer website