gait (human) gait (human) a gait is a pattern of limb movements made during locomotion. human gaits are the various ways in which humans can move, either naturally or as a result of specialized training. human gait is defined as bipedal, biphasic forward propulsion of the center of gravity of the human body, in which there are alternate sinuous movements of different segments of the body with least expenditure of energy. gait patterns are characterized by differences in limb movement patterns, overall velocity, forces, kinetic and potential energy cycles, and changes in contact with the ground. humans using a running gait. the runner in the back and on the far right are in the suspended phase, in which neither foot touches the ground. classification human gaits are classified in various ways. each gait can be generally categorized as either natural (one that humans use instinctively) or trained (a non-instinctive gait learned via training). examples of the latter include hand walking and specialized gaits used in martial arts. gaits can also be categorized according to whether the person remains in continuous contact with the ground. foot strike one variable in gait is foot strike – how the foot contacts the ground, specifically which part of the foot first contacts the ground. forefoot strike – toe-heel: ball of foot lands first mid-foot strike – heel and ball land simultaneously heel strike – heel-toe: heel of foot lands, then plantar flexes to ball in sprinting, gait typically features a forefoot strike, but the heel does not contact the ground. some researchers classify foot strike by the initial center of pressure; this is mostly applicable to shod running (running while wearing shoes). in this classification: a forefoot strike has the initial center of pressure in the front one-third of shoe length; a mid-foot strike is in the middle third; a rear-foot strike (heel strike) is in the rear third. foot strike varies to some degree between strides, and between individuals. it varies significantly and notably between walking and running, and between wearing shoes (shod) and not wearing shoes (barefoot). typically, barefoot walking features heel or mid-foot strike, while barefoot running features mid-foot or forefoot strike. barefoot running rarely features heel strike because the impact can be painful, the human heel pad not absorbing much of the force of impact. by contrast, 75% of runners wearing modern running shoes heel strike; running shoes are characterized by a padded sole, stiff soles and arch support, and slope down from a more-padded heel to a less-padded forefoot. the cause of this change in gait in shoe running is unknown, but lieberman noted that there is correlation between the foot-landing style and exposure to shoes. in some individuals, the gait pattern is largely unchanged – the leg position and foot position are identical in barefoot and shoe running – but the wedge shape of the padding moves the point of impact back from the forefoot to the mid-foot. in other cases, it is believed that the padding of the heel softens the impact and results in runners modifying their gait to move the point of contact further back in the foot. a 2012 study involving harvard university runners found that those who "habitually rear-foot strike had approximately twice the rate of repetitive stress injuries than individuals who habitually forefoot strike". this was the first study that investigated the link between foot strike and injury rates. however, earlier studies have shown that smaller collision forces were generated when running forefoot strike compared to rear-foot strike. this may protect the ankle joints and lower limbs from some of the impact-related injuries experienced by rear-foot strikers. in a 2017 article called "foot strike pattern in children during shod-unshod running", over 700 children aged 6–16 were observed using multiple video recording devices, to study their foot strike patterns and neutral support. rear foot strike was most common, in both shod and unshod running, and in both boys and girls. there was a significant reduction in rear foot strike from shod to unshod: boys shod - 83.95% rfs, boys unshod - 62.65% rfs; girls shod - 87.85% rfs, girls unshod - 62.70% rfs. as-of 2021 there was a very low level of evidence to suggest a relationship between foot strike pattern and runner injury. studies used retrospective designs, low sample size and potentially inaccurate self-reporting. control of gait by the nervous system the central nervous system regulates gait in a highly ordered fashion through a combination of voluntary and automatic processes. the basic locomotor pattern is an automatic process that results from rhythmic reciprocal bursts of flexor and extensor activity. this rhythmic firing is the result of central pattern generators (cpgs), which operate regardless of whether a motion is voluntary or not. cpgs do not require sensory input to be sustained. however, studies have identified that gait patterns in deafferented or immobilized animals are more simplistic than in neurologically intact animals. (deafferentation and immobilization are experimental preparations of animals to study neural control. deafferentation involves transecting the dorsal roots of the spinal cord that innervate the animal's limbs, which impedes transmission of sensory information while keeping motor innervation of muscles intact. in contrast, immobilization involves injecting an acetylcholine inhibitor, which impedes the transmission of motor signals while sensory input is unaffected.) the complexity of gait arises from the need to adapt to expected and unexpected changes in the environment (e.g., changes in walking surface or obstacles). visual, vestibular, proprioceptive, and tactile sensory information provides important feedback related to gait and permits the adjustment of a person's posture or foot placement depending on situational requirements. when approaching an obstacle, visual information about the size and location of the object is used to adapt the stepping pattern. these adjustments involve change in the trajectory of leg movement and the associated postural adjustments required to maintain their balance. vestibular information provides information about position and movement of the head as the person moves through their environment. proprioceptors in the joints and muscles provide information about joint position and changes in muscle length. skin receptors, referred to as exteroceptors, provide additional tactile information about stimuli that a limb encounters. gait in humans is difficult to study due to ethical concerns. therefore, the majority of what is known about gait regulation in humans is ascertained from studies involving other animals or is demonstrated in humans using functional magnetic resonance imaging during the mental imagery of gait. these studies have provided the field with several important discoveries. locomotor centers there are three specific centers within the brain that regulate gait: mesencephalic locomotor region (mlr)- within the midbrain, the mlr receives input from the premotor cortex, the limbic system, cerebellum, hypothalamus, and other parts of the brainstem. these neurons connect to other neurons within the mesencephalic reticular formation which then descend to the via the ventrolateral funiculus to the spinal locomotor networks. studies where the mlr of decerebrate cats have been stimulated either electrically or chemically have shown that increased intensity of stimulation has led to increased speed of stepping. deep brain stimulation of the mlr in individuals with parkinson's has also led to improvements in gait and posture. sub thalamic locomotor region (slr)- the slr is part of hypothalamus. it activates the spinal locomotor networks both directly and indirectly via the mlr. cerebellar locomotor region (clr)- similar to the slr, the clr activates the reticulo-spinal locomotor pathway via direct and indirect projections. these centers are coordinated with the posture control systems within the cerebral hemispheres and the cerebellum. with each behavioral movement, the sensory systems responsible for posture control respond. these signals act on the cerebral cortex, the cerebellum, and the brainstem. many of these pathways are currently under investigation, but some aspects of this control are fairly well understood. regulation by the cerebral cortex sensory input from multiple areas of the cerebral cortex, such as the visual cortex, vestibular cortex, and the primary sensory cortex, is required for skilled locomotor tasks. this information is integrated and transmitted to the supplementary motor area (sma) and premotor area of the cerebral cortex where motor programs are created for intentional limb movement and anticipatory postural adjustments. for example, the motor cortex uses visual information to increase the precision of stepping movements. when approaching an obstacle, an individual will make adjustments to their stepping pattern based on visual input regarding the size and location of the obstacle. the primary motor cortex is responsible for the voluntary control for the contralateral leg while the sma is linked to postural control. regulation by the cerebellum the cerebellum plays a major role in motor coordination, regulating voluntary and involuntary processes. regulation of gait by the cerebellum is referred to as “error/correction,” because the cerebellum responds to abnormalities in posture in order to coordinate proper movement. the cerebellum is thought to receive sensory information (e.g. visual, vestibular) about actual stepping patterns as they occur and compare them to the intended stepping pattern. when there is a discrepancy between these two signals, the cerebellum determines the appropriate correction and relays this information to the brainstem and motor cortex. cerebellar output to the brainstem is thought to be specifically related to postural muscle tone while output to the motor cortex is related to cognitive and motor programming processes. the cerebellum sends signals to the cerebral cortex and the brain stem in response to sensory signals received from the spinal cord. efferent signals from these regions go to the spinal cord where motor neurons are activated to regulate gait. this information is used to regulate balance during stepping and integrates information about limb movement in space, as well as head position and movement. regulation by the spinal cord spinal reflexes not only generate the rhythm of locomotion through cpgs but also ensure postural stability during gait. there are multiple pathways within 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 with the ground (single limb stance), the center of mass is in front of that foot