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Human gait refers to locomotion achieved through the movement of human limbs. Human gait is defined as bipedal, biphasic forward propulsion of 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. Different gait patterns are characterized by differences in limb movement patterns, overall velocity, forces, kinetic and potential energy cycles, and changes in the contact with the surface (ground, floor, etc.). Human gaits are the various ways in which a human can move, either naturally or as a result of specialized training.
Human gaits are classified in various ways. Every 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.
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
· midfoot 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 rearfoot strike (heel strike) has the initial center of pressure in the rear third of the shoe (rear 1/3 of shoe length);
· a midfoot strike is in the middle third (middle 1/3 of shoe length);
· a forefoot strike is in the front third (front 1/3 of shoe length).
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 midfoot strike, while barefoot running features midfoot 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 being characterized by a padded sole, stiff soles and arch support, and sloping down from a more padded heel to a less padded forefoot.
The cause of this change in gait in shoe running is unknown, but Liebermann 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 moving the point of impact back from the forefoot to the midfoot. In other cases, it is conjectured that the padding of the heel softens the impact and resulting in runner modifying their gait to contact further back in the foot.
A 2012 study involving Harvard University runners found that those who "habitually rearfoot 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," there was a study done where over 700 children were observed from the ages of 6-16 to see their foot strike patterns and neutral support. They also wanted to see what outside factors to shod and unshod conditions and sex. This study used multiple video recording devices to get their results. The results showed that most foot patterns such as foot rotation and the rearfoot strike were similar in boys and girls at the same ages.
The CNS regulates gait in a highly ordered fashion. The signals fire in a rhythmic fashion that matches the movement seen in behavior. This rhythmic firing is the result of Central Pattern Generators (CPG) that are present throughout the tracts. Regardless of if a motion is voluntary or not, these processes occur. Therefore, CPG’s are mostly autonomous to cognition.
Gait in humans is difficult to study due to ethical concerns. Therefore, the majority of what is known about gait in humans comes from fMRI data in different walking conditions. These studies have provided the field with several important discoveries.
There are numerous centers, both in the brain and in the spinal cord, that have been proposed to regulate gate. There are three centers that are specifically described to regulate locomotion:
· MLR- Mesopontine Tegmentum Locomotor Region
· SLR- Spinal Cord Locomotor Region
· CLR- Cerebellar Locomotor Region
These centers are coordinated with the posture control systems in place in the cerebral hemisphere 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.
From fMRI studies, two regions have been identified to hold particular importance in gait regulation. These are the supplementary motor area (SMA) and the prefrontal cortex (PFC.) When these regions are inhibited in bi-pedal monkeys, a close relative to humans, they experience irregular gait. In addition, the firing rate of these regions has been shown to regulate speed of gait. This suggestion is the result of a study showing that elderly have less activity in these regions, and this firing rate correlates with a slower gait. How these regions are regulated has yet to be fully elucidated, however they serve as current areas of research for disorders associated with irregular gait, such as Parkinson’s.
The cerebellum plays a major role in motor coordination. 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 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.
There are multiple pathways within the spinal cord which play a role in regulating gait:
· Stretch and Flexion Reflexes- as one footstrike occurs, the spinal cord sends inhibitory signals to the other side so that one side is actively moving forward as the other side is preparing for movement.
· Reciprocal Inhibition- one side of the leg is active as the other is relaxed. There is cross-talk between the two limbs.
· Autoinhibition- when the muscle itself inhibits activity.
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.
The walk is a gait which keeps at least one foot in contact with the ground at all times.
The walk is performed with the following steps:
1. Lift one leg off of the ground;
2. Using the leg in contact with the ground, push your body forward;
3. Swing your lifted leg forward until it is in front of your body;
4. Fall forward to allow your lifted leg to contact the ground;
5. Repeat steps 1–4 for the other leg;
6. Repeat steps 1–5 to continue walking.
In order to investigate the gait strategies likely to be favored at low gravity a series of predictive, computational simulations of gait are performed using a physiological model of the musculoskeletal system, without assuming any particular type of gait; a computationally efficient optimization strategy is utilized allowing for multiple simulations. The results reveal skipping as more efficient and less fatiguing than walking or running and suggest the existence of a walk-skip rather than a walk-run transition at low gravity.
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. 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 increased so did velocity. Meanwhile, as age increases, cadence (rate at which someone walks that is measured in steps per minute) of the gait pattern decreased. 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.
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.
There are gender differences in human gait patterns: females tend to walk with smaller step width and more pelvic movement. Gait analysis generally takes gender into consideration. Gender differences in human gait can be explored using a demonstration created by the Biomotion Laboratory at Queen's University, Kingston, Canada.
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 the human heel-first gait conserves more energy over long distances than other gaits, which is consistent with the belief that humans are evolutionarily specialized for long-distance movement.
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. 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." 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."
Abnormal gait is a result of one or more of these tracts being disturbed. This can happen developmentally or as the result of neurodegeneration. 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. 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.
Although these are the best understood examples of abnormal gait, there are other phenomenons that are described in the medical field.
· 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
· 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.
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