right|Red wolf running.|thumb Running is a 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. 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 running can refer to any of a variety of speeds ranging from jogging to sprinting.

Motion

Humans actually 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 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. Running 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. Fact: date=March 2009 thumb|Jeanette Kwakye during World Indoor Championships 2008 in Valencia|right

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.

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 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. 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 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 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.