the spinal cord which play a role in regulating gait, including the role of reciprocal inhibition and stretch reflexes to produce alternating stepping patterns. A stretch reflex occurs when a muscle is stretched and then contracts protectively while opposing muscle groups relax. An example of this during gait occurs when the weight-bearing leg nears the end of the stance phase. At this point the hip extends and the hip flexors are elongated. Muscle spindles within the hip flexors detect this stretch and trigger muscle contraction of the hip flexors required for the initiation of the swing phase of gait. However, Golgi tendon organs in the extensor muscles also send signals related to the amount of weight being supported through the stance leg to ensure that limb flexion does not occur until the leg is adequately unweighted and the majority of weight has been transferred to the opposite leg. Information from the spinal cord is transmitted for higher order processing to supraspinal structures via spinothalamic, spinoreticular, and spinocerebellar tracts. Natural gaits The so-called natural gaits, in increasing order of speed, are the walk, jog, skip, run, and sprint. While other intermediate speed gaits may occur naturally to some people, these five basic gaits occur naturally across almost all cultures. All natural gaits are designed to propel a person forward but can also be adapted for lateral movement. As natural gaits all have the same purpose; they are mostly distinguished by when the leg muscles are used during the gait cycle. Walk Walking involves having at least one foot in contact with the ground at all times. There is also a period of time within the gait cycle where both feet are simultaneously in contact with the ground. When a foot is lifted off the ground, that limb is in the "swing phase" of gait. When a foot is in contact with the ground, that limb is in the "stance phase" of gait. A mature walking pattern is characterized by the gait cycle being approximately 60% stance phase, 40% swing phase. Initiation of gait is a voluntary process that involves a preparatory postural adjustment where the center of mass is moved forward and laterally prior to unweighting one leg. The center of mass is only within a person's base of support when both feet are in contact with the ground (known as double limb stance). When only one foot is in contact