Gait (human)

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.[3] Gaits can also be categorized according to whether the person remains in continuous contact with the ground.[2]

One variable in gait is foot strike – how the foot contacts the ground, specifically which part of the foot first contacts the ground.[4]

• 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).[5] 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.[4] By contrast, 75% of runners wearing modern running shoes heel strike;[6] 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.[6] In some individuals the gait pattern is largely unchanged (the leg and foot positions are identical in barefoot and shoes), but the wedge shape of the padding moves the point of impact back from the forefoot to the mid-foot.[5] In other cases it is believed that the padding of the heel softens the impact. This results in runners modifying their gait to move the point of contact further back in the foot.[6]

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".[7] 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.[8]

In a 2017 article called "Foot Strike Pattern in Children During Shod-Unshod Running", over 700 children aged 6 to 16 were observed using multiple video recording devices in order 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. [9]

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. [10]

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),[11] 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.)[12]

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.[12]

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.[13] These studies have provided the field with several important discoveries.

The so-called natural gaits, in increasing order of speed, are the walk, jog, skip, run, and sprint.[2][17] 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.[2] As natural gaits all have the same purpose; they are mostly distinguished by when the leg muscles are used during the gait cycle.

Time and distance parameters of gait patterns are dependent on a child's age. Different age leads to different step speed and timing. Arm swinging slows when the speed of walking is increased. The height of a child plays a significant role in stride distance and speed. The taller the child is the longer the stride will be and the further the step will be. Gait patterns are velocity and age dependent. For example, as age increases so does velocity. Meanwhile, as age increases, the cadence (rate at which someone walks that is measured in steps per minute) of the gait pattern decreases. Physical attributes such as height, weight, and even head circumference can also play a role in gait patterns in children. Environmental and emotional status also play a role in with speed, velocity, and gait patterns that a child uses. Besides, children of different genders will have different rates of gait development. Significant developmental changes in gait parameters such as stride time, swing time, and cadence occur in a child's gait two months after the onset of independent walking, possibly due to an increase in postural control at this point of development.[19]

By the age of three, most children have mastered the basic principles of walking, consistent with that of adults. Age is not the only deciding factor in gait development. Gender differences have been seen in young children as early as three years old. Girls tend to have a more stable gait than boys between the ages of 3–6 years old. Another difference includes the plantar contact area. Girls showed a smaller contact area in plantar loading patterns than boys in children with healthy feet.[19]

There are sex differences in human gait patterns: females tend to walk with smaller step width and more pelvic movement.[20] Gait analysis generally takes biological sex into consideration.[21] Sex differences in human gait can be explored using a demonstration created by the BioMotion Laboratory at York University in Toronto.[22]

Even though plantigrade locomotion usually distributes more weight toward the end of the limb than digitigrade locomotion, which increases energy expenditure in most systems, studies have shown that humans are economical walkers, but not economical runners, which is said to be consistent with evolutionary specialization for both economical walking and endurance running.[23]

For the same distance, walking with a natural heel-first gait burns roughly 70% less energy than running. Differences of this magnitude are unusual in mammals.[23] Kathyrn Knight of the Journal of Experimental Biology summarizes the findings of one study: "Landing heel first also allows us to transfer more energy from one step to the next to improve our efficiency, while placing the foot flat on the ground reduces the forces around the ankle (generated by the ground pushing against us), which our muscles have to counteract."[24] According to David Carrier of the University of Utah, who helped perform the study, "Given the great distances hunter-gatherers travel, it is not surprising that humans are economical walkers."[23]

A normal gait pattern depends on a range of biomechanical features, controlled by the nervous system for increased energy conservation and balance.[25] These biomechanical features of normal gait have been defined as key determinants of gait. It is therefore necessary for the refined neurological control and integration of these gait features for accuracy and precision with less energy expenditure. As a result, any abnormality of the neuro-musculo-skeletal system may lead to abnormality in gait and increased energy expenditure.

The six kinematics or determinants of gait, described below, were introduced by Saunders et al. in 1953,[26] and have been widely embraced with various refinements.[27][28][29][30][31] Recent studies have suggested that the first three determinants might contribute less to reducing the vertical displacement of the center of mass (COM).

These determinants of gait are known to ensure economical locomotion,[25] by the reduction in vertical center of mass (COM) excursion leading to reduction in metabolic energy. It is therefore suggested that the precise control of these determinants of gait[32] leads to increased energy conservation. These kinematic features of gait are integrated or coordinated in order to ensure a circular arc trajectory of the COM, as theory proposed as the 'compass gait (straight knee)'. The theory underlying the determinants run contrary to that of the 'inverted pendulum' theory with a static stance leg acting as a pendulum that prescribes an arc.[33][34][35] The six determinants of gaits and their effects on COM displacement and energy conservation are described below in chronological order:

1. Pelvic rotation: This kinematic feature of gait operates under the theory of compass gait model.[36] In this model, the pelvis rotates side to side during normal gait. In effect, it aids in the progression of the contralateral side through reduced hip flexion and extension. Its effect on the reduction of metabolic energy and the increased energy conservation is through the reduction of vertical COM displacement. This notion of reduction of metabolic cost may be disputed by a study done by Gard and Childress (1997),[37] who stated that there may be minimal effect of pelvic rotation on vertical COM displacement. Furthermore, other studies have found pelvic rotation to have little effect on the smoothing of COM trajectory.[25] Pelvic rotation has been shown to account for about 12% reduction in the total COM vertical displacement.[36]
2. Pelvic tilt/Obliquity: Normal gait results in tilting of the swing phase side, in relation to the control by the stance side hip abductors. As a consequence, there is the neutralization of raising of COM during the transition from hip flexion to extension. Its effect on the reduction of metabolic energy and the increased energy conservation is via the reduction of vertical COM trajectory or peak form compass gait model. Pelvic obliquity's effects on reduction of vertical displacement of COM has been examined and been shown to only reduce vertical displacement of COM by at most, only 2–4 mm.[37]
3. Knee flexion at stance phase: The knee usually supports the body weight in flexed position during walking. The knee is usually fully extended at heel strike and then begins to flex (average magnitude of 15 degrees) when foot is completely flat on the ground. The effects of the stance-phase knee flexion is to lower the apex of vertical trajectory of the COM via shortening of the leg resulting in some energy conservation.[26] But recent studies testing this third determinant of gait have reported varied results. It was found out that stance-phase knee flexion did not contribute to the reduction in vertical trajectory of COM.[25] Furthermore, Gard and Childress (1997) indicated that maximum COM is reached at mid-stance when knee is slightly flexed, depicting minor reduction of the maximum height of the COM by a few millimeters.[37]
4. Foot and ankle motions: Saunders et al. showed relationship between angular displacement and motions of foot, ankle and knee.[26] This results in two intersecting arcs of rotation at the foot during stance phase at heel contact and heel rise. At heel contact the COM reaches its lowest point of downward displacement when the foot is dorsiflexed, and the knee joint fully extended in order for the extremity to be at its maximum length. The ankle rockers at heel strike and mid-stance leads to decrease COM displacement through the shortening of the leg. Studies by Kerrigan et al. (2001) and Gard & Childress (1997) have showed the major role played by heel rise in reducing the COM vertical displacement.[37][38]
5. Knee motion: The motion of the knee is related to those of the ankle and foot motions and results in the reduction of COM vertical displacement. Therefore, an immobile knee or ankle could lead to increases in COM displacement and energy cost.
6. Lateral pelvic displacement: In this key gait feature, the displacement of the COM is realized by the lateral shift of the pelvis or by relative adduction of the hip. Correction of disproportionate lateral displacement of the pelvis is mediated by the effect of tibiofemoral angle, and relative adduction of the hip, which results in reduction in vertical COM displacement.[26] It is clear that these kinematic features play a critical role in ensuring efficiency in normal gait. But there may be the need for further extensive testing or validation of each of the key determinants of gait.

Abnormal gait is a result of one or more of these tracts being disturbed. This can happen developmentally or as the result of neurodegeneration.[11] The most prominent example of gait irregularities due to developmental problems comes from studies of children on the autism spectrum. They have decreased muscle coordination, thus resulting in abnormalities in gait.[39] Some of this is associated with decreased muscle tone, also known as hypotonia, which is also common in ASD. The most prominent example of abnormal gait as a result of neurodegeneration is Parkinson's.[11]

Although these are the best understood examples of abnormal gait, there are other phenomena that are described in the medical field.[40]

• Antalgic gait: limping caused by pain that appears or worsens when bearing weight on one limb, due to injury, disease, or other painful conditions
• Charlie Chaplin gait: occurs in tibial torsion.
• Circumduction gait: occurs in hemiplegia
• Waddling gait: occurs in bilateral congenital hip dislocation
• High stepping gait: occurs in foot drop
• Scissor gait: occurs in cerebral palsy
• Stiff hip gait: occurs in ankylosis of the hip
• Trendelenburg gait: occurs in unstable hip due to congenital dislocation of hip, gluteus medius muscle weakness

Abnormal gait can also be a result of a stroke. However, by using treadmill therapy to activate the cerebellum, abnormalities in gait can be improved.

The author of the Deuterocanonical Book of Sirach observes that "a man's attire, and excessive laughter, and gait, shew what he is".[41] Bibilical writer J. J. Collins suggests that this verse quotes a traditional maxim.[42]

• Astasia abasia
• Contrapposto
• Gait abnormality
• Gait Abnormality Rating Scale
• Gait analysis
• Human positions
• Marche a petit pas
• Power walking
• Soft biometrics
• Terrestrial locomotion in animals

The dictionary definition of gait at Wiktionary