Gait analysis

Gait analysis is the systematic study of animal locomotion, more specific as a study of human motion, using the eye and the brain of observers, augmented by instrumentation for measuring body movements, body mechanics, and the activity of the muscles. Gait analysis is used to assess, plan, and treat individuals with conditions affecting their ability to walk. It is also commonly used in sports biomechanics to help athletes run more efficiently and to identify posture-related or movement-related problems in people with injuries.

The study encompasses quantification, i.e. introduction and analysis of measurable parameters of gaits, as well as interpretation, i.e. drawing various conclusions about the animal (health, age, size, weight, speed, etc.) from its gait.

History
The pioneers of scientific gait analysis were Aristotle in De Motu Animalium (On the Gait of Animals) and much later in 1680, Giovanni Alfonso Borelli also called De Motu Animalium (I et II). In the 1890s, the German anatomist Christian Wilhelm Braune and Otto Fischer published a series of papers on the biomechanics of human gait under loaded and unloaded conditions.

With the development of photography and cinematography, it became possible to capture image sequences that revealed details of human and animal locomotion that were not noticeable by watching the movement with the naked eye. Eadweard Muybridge and Étienne-Jules Marey were pioneers of these developements in the early 1900s. For example, serial photography first revealed the detailed sequence of the horse "gallop", which was usually misrepresented in paintings made prior to this discovery.

Although much early research was done using film cameras, the widespread application of gait analysis to humans with pathological conditions such as cerebral palsy, Parkinson's disease, and neuromuscular disorders, began in the 1970s with the availability of video camera systems that could produce detailed studies of individual patients within realistic cost and time constraints. The development of treatment regimes, often involving orthopaedic surgery, based on gait analysis results, advanced significantly in the 1980s. Many leading orthopaedic hospitals worldwide now have gait labs that are routinely used to design treatment plans and for follow-up monitoring.

Development of modern computer based systems occurred independently during the late 1970s and early 1980s in several hospital based research labs, some through collaborations with the aerospace industry. Commercial development soon followed with the emergence of commercial television and later infrared camera systems in the mid-1980s.

Process and equipment
A typical gait analysis laboratory has several cameras (video and / or infrared) placed around a walkway or a treadmill, which are linked to a computer. The patient has markers located at various points of reference of the body (e.g. iliac spines of the pelvis, ankle malleolus, and the condyles of the knee), or groups of markers applied to half of the body segments. The patient walks down the catwalk or the treadmill and the computer calculates the trajectory of each marker in three dimensions. A model is applied to calculate the movement of the underlying bones. This gives a complete breakdown of the movement of each joint.

To calculate the kinetics, most labs have floor-mounted load transducers, also known as force platforms, which measure the ground reaction forces and moments, including the magnitude, direction and location (called the center of pressure). The spatial distribution of forces can be measured with pedobarography equipment. Adding this to the known dynamics of each body segment, enables the solution of equations based on the Newton–Euler equations of motion permitting computations of the net forces and the net moments of force about each joint at every stage of the gait cycle. The computational method for this is known as inverse dynamics.

This use of kinetics, however, does not result in information for individual muscles but muscle groups, such as the extensor or flexors of the limb. To detect the activity and contribution of individual muscles to movement, it is necessary to investigate the electrical activity of muscles. Many labs also use surface electrodes attached to the skin to detect the electrical activity or electromyogram (EMG) of, for example, a muscles of the leg. In this way it is possible to investigate the activation times of muscles and, to some degree, the magnitude of their activation—thereby assessing their contribution to gait. Deviations from normal kinematic, kinetic, or EMG patterns are used to diagnose specific pathologies, predict the outcome of treatments, or determine the effectiveness of training programs

Factors and parameters
The gait analysis is modulated or modified by many factors, and changes in the normal gait pattern can be transient or permanent. The factors can be of various types:
 * Extrinsic: Several extrinsic factors such as terrain, footwear, clothing, cargo
 * Intrinsic: Intrinsic factors are sex (male and female), weight, height, age, etc.
 * Physical: Physical factors such is the weight, height, physique
 * Psychological: Psychological factors are the type of personality, emotions
 * Physiological: When talking about is physiological anthropometric characteristics
 * Pathologic, pathological factors can be for example trauma, neurological diseases, musculoskeletal, psychiatric disorders

The parameters taken into account for the gait analysis are the following:
 * Step length
 * Stride length
 * Cadence
 * Speed​​
 * Dynamic Base
 * Progression Line
 * Foot Angle

Techniques
The study includes the measurement, i.e. introduction and analysis of measurable parameters, and the interpretation, i.e., reach different conclusions about the person (health, age, size, weight, speed, etc..) The gait analysis is the measurement of the following:

Temporal / spatial
It consists in the calculation of "speed, the length of the rhythm, pitch, and so on. These measurements are carried out through:
 * Stopwatch and marks on the ground.
 * March on a pressure mat.

Kinematics

 * 1) Chronophotography is the most basic method for the recording of movement. Strobe lighting at known frequency has been used in the past to aid in the analysis of gait on single photographic images.
 * 2) Cine film or video recordings using footage from single or multiple cameras can be used to measure joint angles and velocities. This method has been aided by the development of analysis software that greatly simplifies the analysis process and allows for analysis in three dimensions rather than two dimensions only.
 * 3) Passive marker systems, using reflective markers (typically reflective balls), allows for very accurate measurement of movements using multiple cameras (typically five to twelve cameras), simultaneously. The cameras utilize high-powered strobes (typically red, near infrared or infrared) with matching filters to record the reflection from the markers placed on the body. Markers are located at palpable anatomical landmarks. Based on the angle and time delay between the original and reflected signal, triangulation of the marker in space is possible. Software is used to create three dimensional trajectories from these markers which are subsequently given identification labels. A computer model is then used to compute joint angles from the relative marker positions of the labeled trajectories. These are also used for motion capture in the motion picture industry.
 * 4) Active marker systems are similar to the passive marker system but use "active" markers. These markers are triggered by the incoming infra red signal and respond by sending out a corresponding signal of their own. This signal is then used to triangulate the location of the marker. The advantage of this system over the passive one is that individual markers work at predefined frequencies and therefore, have their own "identity". This means that no post-processing of marker locations is required, however, the systems tend to be less forgiving for out-of-view markers than the passive systems.
 * 5) Inertial (cameraless) systems based on MEMS inertial sensors, biomechanical models, and sensor fusion algorithms. These full-body or partial body systems can be used indoors and outdoors regardless of lighting conditions.

Kinetics
Is the study of the forces involved in the production of these movements.

Dynamic Electromyography
Is the study of patterns of muscle activity during gait.

Applications
Gait analysis is used to analyze the walking ability of humans and animals, so this technology can be used for the following applications:

Medical diagnostics
Pathological gait may reflect compensations for underlying pathologies, or be responsible for causation of symptoms in itself. Cerebral palsy and stroke patients are commonly seen in gait labs. The study of gait allows diagnoses and intervention strategies to be made, as well as permitting future developments in rehabilitation engineering. Aside from clinical applications, gait analysis is used in professional sports training to optimize and improve athletic performance.

Gait analysis techniques allow for the assessment of gait disorders and the effects of corrective Orthopedic surgery. Options for treatment of cerebral palsy include the paralysis of spastic muscles using Botox or the lengthening, re-attachment or detachment of particular tendons. Corrections of distorted bony anatomy are also undertaken (osteotomy).

Biometric identification and forensics
Minor variations in gait style can be used as a biometric identifier to identify individual people. The parameters are grouped to spatial-temporal (step length, step width, walking speed, cycle time) and kinematic (joint rotation of the hip, knee and ankle, mean joint angles of the hip/knee/ankle, and thigh/trunk/foot angles) classes. There is a high correlation between step length and height of a person.

The English XL slip meter, also known as a VIT (Variable Incidence Tribometer) is a leading edge portable "slip tester", which is designed to test the coefficient of friction or "slip index" on various walking surfaces, level or incline (even steps), under dry and wet (or otherwise contaminated) conditions by mimicking certain pedestrian biomechanical parameters. The objective measurements that can be analyzed and compared with "normal" walking forces and industry standards regarding flooring slip resistance.

Comparative biomechanics
By studying the gait of non-human animals, more insight can be gained about the mechanics of locomotion, which has diverse implications for understanding the biology of the species in question as well as locomotion more broadly.

Related Videos

 * Video explaining the concept of gait analysis and practical example


 * Video explaining how to perform the gait analysis


 * Video explaining how and why the company Currex, performed the analysis of their customers up


 * Video example of reading an analysis of foot pressure on a moving subject


 * Video example of the movement that made ​​the muscles of the body when we walk


 * Example of different graphs obtained from the gait analysis by Animazoo Motion Capture

Popular media

 * G. K. Chesterton premised one of his Father Brown mysteries, "The Queer Feet", on gait recognition.
 * Cory Doctorow makes much of gait recognition as a security technique used in a high school in his book Little Brother.