Gait (human)

thumb|250px|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.

thumb|250px|Rear-foot strike also known as "heel strike"

A gait is a manner 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 forward propulsion of the center of gravity of the human body, in which there are sinuous movements of different segments of the body with little energy spent. Various gaits are characterized by differences in limb movement patterns, overall velocity, forces, kinetic and potential energy cycles, and changes in contact with 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.

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

Sprinting typically features a forefoot strike, but the heel does not usually 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 between types of strides. It changes 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 strikes, while barefoot running features mid-foot or forefoot strikes. Barefoot running rarely features heel strikes because the impact can be painful, the human heel pad not absorbing much of the force of impact. 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. This was the first study to investigate 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 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.

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. These studies have provided the field with several important discoveries.

Locomotor centers

There are three specific centers within the brain that regulate gait: 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. 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. 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. 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 and moving towards the leg that is in the swing phase.

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. Gait analysis generally takes biological sex into consideration. Sex differences in human gait can be explored using a demonstration created by the BioMotion Laboratory at York University in Toronto.

Efficiency and evolutionary implications

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.

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. 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." 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, and have been widely embraced with various refinements. 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, 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. The six determinants of gaits and their effects on COM displacement and energy conservation are described below in chronological order:

Pelvic rotation: This kinematic feature of gait operates under the theory of compass gait model. 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), 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.
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.
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. 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.

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.

Literary references

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

Classification

Control of gait by the nervous system

Locomotor centers

Efficiency and evolutionary implications

Literary references

See also

References