Gait analysis

Last updated

Acquisition of information on the position of the markers in 2D through the chambers of the left and right, this combination of information giving rise to a 3D image on the position of the markers Proce.jpg
Acquisition of information on the position of the markers in 2D through the chambers of the left and right, this combination of information giving rise to a 3D image on the position of the markers

Gait analysis is the systematic study of animal locomotion, more specifically the 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. [1] Gait analysis is used to assess 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.

Contents

The study encompasses quantification (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 pattern.

History

The pioneers of scientific gait analysis were Aristotle in De Motu Animalium (On the Gait of Animals) [2] 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. [3]

Medical gait photography, 1918 Medical and surgical therapy (1918) (14781804412).jpg
Medical gait photography, 1918

With the development of photography and cinematography, it became possible to capture image sequences that reveal 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 developments 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 orthopedic surgery, based on gait analysis results, advanced significantly in the 1980s. Many leading orthopedic hospitals worldwide now have gait labs that are routinely used to design treatment plans and for follow-up monitoring.[ citation needed ]

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. [4] Commercial development soon followed with the emergence of commercial television and later infrared camera systems in the mid-1980s.

In 2018 there is a new proposal for a kinetic summary measure, the Gait Kinetic Index.

Process and equipment

Gait analysis laboratory equipped with infrared cameras and floor mounted force platforms Gait laboratory.jpg
Gait analysis laboratory equipped with infrared cameras and floor mounted force platforms

A typical gait analysis laboratory has several cameras (video 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. One common method is to use Helen Hayes Hospital marker set, [5] in which a total of 15 markers are attached on the lower body. The 15 marker motions are analyzed analytically, and it provides angular motion of each joint.[ citation needed ]

To calculate the kinetics of gait patterns, 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.[ citation needed ]

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 muscles. 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[ citation needed ]

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:

The parameters taken into account for the gait analysis are as follows:

Techniques

Walking sequences recorded by motion capture Two repetitions of a walking sequence of an individual recorded using a motion-capture system.gif
Walking sequences recorded by motion capture

Gait analysis involves measurement, [7] where measurable parameters are introduced and analyzed, and interpretation, where conclusions about the subject (health, age, size, weight, speed, etc.) are drawn. The analysis is the measurement of the following:

Temporal / spatial

It consists of the calculation of speed, the length of the rhythm, pitch, and so on. These measurements are carried out through:

Kinematics

  1. Chronophotography is the most basic method for 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. [10] [11]
  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 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 that are subsequently given identification labels. A computer model is then used to compute joint angles from the relative marker positions of the labeled trajectories. [12] These are also used for motion capture in the motion picture industry. [13]
  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. [14]
  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.

Markerless gait capture

Pressure measurement

Pressure measurement systems are an additional way to measure gait by providing insights into pressure distribution, contact area, center of force movement and symmetry between sides. These systems typically provide more than just pressure information; additional information available from these systems are force, timing and spatial parameters. Different methods for assessing pressure are available, like a pressure measurement mat or walkway (longer in length to capture more foot strikes), as well as in-shoe pressure measurement systems (where sensors are placed inside the shoe). [17] [18] [19] Many pressure measurement systems integrate with additional types of analysis systems, like motion capture, EMG or force plates to provide a comprehensive gait analysis.[ citation needed ]

Kinetics

Is the study of the forces involved in the production of 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. [20] Options for treatment of cerebral palsy include the artificial 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). [20]

Chiropractic and osteopathic uses

Observation of gait is also beneficial for diagnoses in chiropractic and osteopathic professions as hindrances in gait may be indicative of a misaligned pelvis or sacrum. As the sacrum and ilium biomechanically move in opposition to each other, adhesions between the two of them via the sacrospinous or sacrotuberous ligaments (among others) may suggest a rotated pelvis. Both doctors of chiropractic and osteopathic medicine use gait to discern the listing of a pelvis and can employ various techniques to restore a full range of motion to areas involved in ambulatory movement. Chiropractic adjustment of the pelvis has shown a trend in helping restore gait patterns [21] [22] as has osteopathic manipulative therapy (OMT). [23] [24]

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.

Gait as biometrics

Gait recognition is a type of behavioral biometric authentication that recognizes and verifies people by their walking style and pace. [25] [26] Advances in gait recognition have led to the development of techniques for forensics use since each person can have a gait defined by unique measurements such as the locations of ankle, knee, and hip. [27]

Surveillance

In 2018, there were reports that the Government of China had developed surveillance tools based on gait analysis, allowing them to uniquely identify people, even if their faces are obscured. [28] [29]

See also

Related Research Articles

<span class="mw-page-title-main">Tremor</span> Involuntary muscle contraction

A tremor is an involuntary, somewhat rhythmic, muscle contraction and relaxation involving oscillations or twitching movements of one or more body parts. It is the most common of all involuntary movements and can affect the hands, arms, eyes, face, head, vocal folds, trunk, and legs. Most tremors occur in the hands. In some people, a tremor is a symptom of another neurological disorder.

<span class="mw-page-title-main">Biomechanics</span> Study of the mechanics of biological systems

Biomechanics is the study of the structure, function and motion of the mechanical aspects of biological systems, at any level from whole organisms to organs, cells and cell organelles, using the methods of mechanics. Biomechanics is a branch of biophysics.

<span class="mw-page-title-main">Motion capture</span> Process of recording the movement of objects or people

Motion capture is the process of recording the movement of objects or people. It is used in military, entertainment, sports, medical applications, and for validation of computer vision and robots. In filmmaking and video game development, it refers to recording actions of human actors and using that information to animate digital character models in 2D or 3D computer animation. When it includes face and fingers or captures subtle expressions, it is often referred to as performance capture. In many fields, motion capture is sometimes called motion tracking, but in filmmaking and games, motion tracking usually refers more to match moving.

<span class="mw-page-title-main">Gait (human)</span> A pattern of limb movements made during locomotion

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. Varied gaits are characterized by differences such as limb movement patterns, overall velocity, forces, kinetic and potential energy cycles, and changes in contact with the ground.

Václav Vojta was a renowned Czech medical doctor who specialized in the treatment of children with cerebral palsy and developmental disorders. He discovered the principle of reflex locomotion, which is used to treat various physical and neuromuscular disorders through the stimulation of the human sensomotoric system's reflex points. Originally used in the treatment of spastic children, the technique is now used on babies and adults.

<span class="mw-page-title-main">Spinal adjustment</span>

Spinal adjustment and chiropractic adjustment are terms used by chiropractors to describe their approaches to spinal manipulation, as well as some osteopaths, who use the term adjustment. Despite anecdotal success, there is no scientific evidence that spinal adjustment is effective against disease.

Inverse dynamics is an inverse problem. It commonly refers to either inverse rigid body dynamics or inverse structural dynamics. Inverse rigid-body dynamics is a method for computing forces and/or moments of force (torques) based on the kinematics (motion) of a body and the body's inertial properties. Typically it uses link-segment models to represent the mechanical behaviour of interconnected segments, such as the limbs of humans or animals or the joint extensions of robots, where given the kinematics of the various parts, inverse dynamics derives the minimum forces and moments responsible for the individual movements. In practice, inverse dynamics computes these internal moments and forces from measurements of the motion of limbs and external forces such as ground reaction forces, under a special set of assumptions.

A facultative biped is an animal that is capable of walking or running on two legs (bipedal), as a response to exceptional circumstances (facultative), while normally walking or running on four limbs or more. In contrast, obligate bipedalism is where walking or running on two legs is the primary method of locomotion. Facultative bipedalism has been observed in several families of lizards and multiple species of primates, including sifakas, capuchin monkeys, baboons, gibbons, gorillas, bonobos and chimpanzees. Different facultatively bipedal species employ different types of bipedalism corresponding to the varying reasons they have for engaging in facultative bipedalism. In primates, bipedalism is often associated with food gathering and transport. In lizards, it has been debated whether bipedal locomotion is an advantage for speed and energy conservation or whether it is governed solely by the mechanics of the acceleration and lizard's center of mass. Facultative bipedalism is often divided into high-speed (lizards) and low-speed (gibbons), but some species cannot be easily categorized into one of these two. Facultative bipedalism has also been observed in cockroaches and some desert rodents.

Motion analysis is used in computer vision, image processing, high-speed photography and machine vision that studies methods and applications in which two or more consecutive images from an image sequences, e.g., produced by a video camera or high-speed camera, are processed to produce information based on the apparent motion in the images. In some applications, the camera is fixed relative to the scene and objects are moving around in the scene, in some applications the scene is more or less fixed and the camera is moving, and in some cases both the camera and the scene are moving.

<span class="mw-page-title-main">Force platform</span>

Force platforms or force plates are measuring instruments that measure the ground reaction forces generated by a body standing on or moving across them, to quantify balance, gait and other parameters of biomechanics. Most common areas of application are medicine and sports.

Equinalysis is a computer software program designed to capture and analyse equine locomotion by visually tracking and quantifying biomechanical data. The system was developed in 2004 by consultant farrier, Haydn Price with the intent of allowing veterinarians, farriers, horse trainers and physiotherapists to highlight subtle changes in a horse's locomotion and provide a video record of how a horse's movements change during the course of its working life. This then allows the user to improve the horse's performance with various techniques and treatment plans, such as appropriate shoeing regimes.

<span class="mw-page-title-main">Pedobarography</span> Study of pressure fields between foot and a supporting surface

Pedobarography is the study of pressure fields acting between the plantar surface of the foot and a supporting surface. Used most often for biomechanical analysis of gait and posture, pedobarography is employed in a wide range of applications including sports biomechanics and gait biometrics. The term 'pedobarography' is derived from the Latin: pedes, referring to the foot, and the Greek: baros meaning 'weight' and also 'pressure'.

<span class="mw-page-title-main">Undulatory locomotion</span>

Undulatory locomotion is the type of motion characterized by wave-like movement patterns that act to propel an animal forward. Examples of this type of gait include crawling in snakes, or swimming in the lamprey. Although this is typically the type of gait utilized by limbless animals, some creatures with limbs, such as the salamander, forgo use of their legs in certain environments and exhibit undulatory locomotion. In robotics this movement strategy is studied in order to create novel robotic devices capable of traversing a variety of environments.

<span class="mw-page-title-main">Neuromechanics of idiopathic scoliosis</span>

The neuromechanics of idiopathic scoliosis is about the changes in the bones, muscles and joints in cases of spinal deformity consisting of a lateral curvature scoliosis and a rotation of the vertebrae within the curve, that is not explained by either congenital vertebral abnormalities, or neuromuscular disorders such as muscular dystrophy. The idiopathic scoliosis accounts for 80–90% of scoliosis cases. Its pathogenesis is unknown. However, changes in the vestibular system, a lateral shift of the hand representation and abnormal variability of erector spinae motor map location in the motor cortex may be involved in this disease. A short spinal cord and associated nerve tensions has been proposed as a cause and model for idiopathic scoliosis. Besides idiopathic scoliosis being more frequent in certain families, it is suspected to be transmitted via autosomal dominant inheritance. Estrogens could also play a crucial part in the progression of idiopathic scoliosis through their roles in bone formation, growth, maturation and turnover. Finally, collagen, intervertebral disc and muscle abnormalities have been suggested as the cause in idiopathic scoliosis, although these are perhaps results rather than causes.

<span class="mw-page-title-main">David A. Winter</span>

David A. Winter is a distinguished professor emeritus of the University of Waterloo. He was a founding member of the Canadian Society for Biomechanics and its first Career Award winner. He was later awarded the Muybridge Medal of the International Society of Biomechanics (ISB) and the Lifetime Achievement Award of The Gait and Clinical Movement Analysis Society. Before becoming an academic he served as an electrical officer with the Royal Canadian Navy on HMCS Nootka from 1952 to 1958. He completed his service at the rank of lieutenant commander. In December 2011, ISB named an award to encourage young people to stay involved in biomechanics research the "David Winter Young Investigator Award."

<span class="mw-page-title-main">Arm swing in human locomotion</span>

Arm swing in human bipedal walking is a natural motion wherein each arm swings with the motion of the opposing leg. Swinging arms in an opposing direction with respect to the lower limb reduces the angular momentum of the body, balancing the rotational motion produced during walking. Although such pendulum-like motion of arms is not essential for walking, recent studies point that arm swing improves the stability and energy efficiency in human locomotion. Those positive effects of arm swing have been utilized in sports, especially in racewalking and sprinting.

Neuromechanics of orthoses refers to how the human body interacts with orthoses. Millions of people in the U.S. suffer from stroke, multiple sclerosis, postpolio, spinal cord injuries, or various other ailments that benefit from the use of orthoses. Insofar as active orthoses and powered exoskeletons are concerned, the technology to build these devices is improving rapidly, but little research has been done on the human side of these human-machine interfaces.

<span class="mw-page-title-main">Proportional myoelectric control</span>

Proportional myoelectric control can be used to activate robotic lower limb exoskeletons. A proportional myoelectric control system utilizes a microcontroller or computer that inputs electromyography (EMG) signals from sensors on the leg muscle(s) and then activates the corresponding joint actuator(s) proportionally to the EMG signal.

X-ray motion analysis is a technique used to track the movement of objects using X-rays. This is done by placing the subject to be imaged in the center of the X-ray beam and recording the motion using an image intensifier and a high-speed camera, allowing for high quality videos sampled many times per second. Depending on the settings of the X-rays, this technique can visualize specific structures in an object, such as bones or cartilage. X-ray motion analysis can be used to perform gait analysis, analyze joint movement, or record the motion of bones obscured by soft tissue. The ability to measure skeletal motions is a key aspect to one's understanding of vertebrate biomechanics, energetics, and motor control.

The study of animal locomotion is a branch of biology that investigates and quantifies how animals move.

References

  1. Levine DF, Richards J, Whittle M. (2012). Whittle's Gait Analysis Whittle's Gait Analysis Elsevier Health Sciences. ISBN   978-0702042652
  2. Aristotle (2004). On the Gait of Animals. Kessinger Publishing. ISBN   978-1-4191-3867-6.
  3. Fischer, Otto; Braune, Wilhelm (1895). Der Gang des Menschen: Versuche am unbelasteten und belasteten Menschen, Band 1 (in German). Hirzel Verlag.
  4. Sutherland DH (2002). "The evolution of clinical gait analysis: Part II Kinematics". Gait & Posture. 16 (2): 159–179. CiteSeerX   10.1.1.626.9851 . doi:10.1016/s0966-6362(02)00004-8. PMID   12297257.
  5. Kadaba, M. P.; Ramakrishnan, H. K.; Wootten, M. E. (May 1990). "Measurement of lower extremity kinematics during level walking". Journal of Orthopaedic Research. 8 (3): 383–392. doi: 10.1002/jor.1100080310 . PMID   2324857. S2CID   17094196.
  6. Schweitzer, Eric. "What is a gait analysis?". IdealRun.
  7. U. Tasch, P. Moubarak, W. Tang, L. Zhu, R.M. Lovering, J. Roche, R. J. Bloch. (2008). An Instrument that Simultaneously Measures Spatiotemporal Gait Parameters and Ground Reaction Forces in Locomoting Rats, in Proceeding of 9th Biennial ASME conference on Engineering Systems Design & Analysis, ESDA ‘08. Haifa, Israel, pp. 45–49.
  8. Piérard, S.; Azrour, S.; Phan-Ba, R.; Van Droogenbroeck, M. (October 2013). "GAIMS: A reliable non-intrusive gait measuring system". ERCIM News. 95: 26–27.
  9. "The GAIMS project".
  10. Étienne-Jules Marey
  11. Eadweard Muybridge
  12. Davis RB, Õunpuu S, Tyburski D, Gage JR (1991). "A gait analysis data collection and reduction technique". Human Movement Science. 10 (5): 575–587. doi:10.1016/0167-9457(91)90046-z.
  13. Robertson DGE, et al. (2004). Research Methods in Biomechanics. Champaign IL:Human Kinetics Pubs.
  14. Best, Russell; Begg, Rezaul (2006). "Overview of Movement Analysis and Gait Features". In Begg, Rezaul; Palaniswami, Marimuthu (eds.). Computational Intelligence for Movement Sciences: Neural Networks and Other Emerging Techniques. Idea Group (published 30 March 2006). pp. 11–18. ISBN   978-1-59140-836-9.
  15. X. Zhang, M. Ding, G. Fan (2016) Video-based Human Walking Estimation by Using Joint Gait and Pose Manifolds, IEEE Transactions on Circuits and Systems for Video Technology, 2016
  16. "Research – Meng Ding".
  17. "Gait Analysis with Pressure Measurement". Tekscan. 9 June 2017. Retrieved 29 September 2017.
  18. Coda, A.; Carline, T.; Santos, D. (2014). "Repeatability and reproducibility of the Tekscan HR-Walkway system in healthy children". Foot (Edinb). 24 (2): 49–55. doi:10.1016/j.foot.2014.02.004. PMID   24703061.
  19. "SCIENCE Insole3 Overview - Moticon" . Retrieved 18 December 2020.
  20. 1 2 Amen, John; ElGebeily, Mohamed; El.Mikkawy, DaliaM. E.; Yousry, AhmedH; El-Sobky, TamerA (2018). "Single-event multilevel surgery for crouching cerebral palsy children: Correlations with quality of life and functional mobility". Journal of Musculoskeletal Surgery and Research. 2 (4): 148. doi:10.4103/jmsr.jmsr_48_18. S2CID   81725776.
  21. Herzog, W (1988). "Quantifying the effects of spinal manipulations on gait using patients with low back pain". Journal of Manipulative and Physiological Therapeutics. 11 (3): 151–157. PMID   2969026.
  22. RO, Robinson; W, Herzog; BM, Nigg (1 August 1987). "Use of force platform variables to quantify the effects of chiropractic manipulation on gait symmetry". Journal of Manipulative and Physiological Therapeutics. 10 (4): 172–6. ISSN   0161-4754. PMID   2958572.
  23. MR, Wells; S, Giantinoto; D, D'Agate; RD, Areman; EA, Fazzini; D, Dowling; A, Bosak (1 February 1999). "Standard osteopathic manipulative treatment acutely improves gait performance in patients with Parkinson's disease". The Journal of the American Osteopathic Association. 99 (2): 92–8. doi: 10.7556/jaoa.1999.99.2.92 . ISSN   0098-6151. PMID   10079641.
  24. Vismara, Luca; Cimolin, Veronica; Galli, Manuela; Grugni, Graziano; Ancillao, Andrea; Capodaglio, Paolo (March 2016). "Osteopathic Manipulative Treatment improves gait pattern and posture in adult patients with Prader–Willi syndrome". International Journal of Osteopathic Medicine. 19: 35–43. doi:10.1016/j.ijosm.2015.09.001.
  25. Alzubaidi, Abdulaziz; Kalita, Jugal (2016). "Authentication of Smartphone Users Using Behavioral Biometrics". IEEE Communications Surveys & Tutorials. 18 (3): 1998–2026. arXiv: 1911.04104 . doi:10.1109/comst.2016.2537748. ISSN   1553-877X. S2CID   8443300.
  26. "Advances in automatic gait recognition – IEEE Conference Publication" (PDF). doi:10.1109/AFGR.2004.1301521. S2CID   13304163.{{cite journal}}: Cite journal requires |journal= (help)
  27. Bouchrika, Imed; Goffredo, Michaela; Carter, John; Nixon, Mark (July 2011). "On using gait in forensic biometrics". Journal of Forensic Sciences. 56 (4): 882–889. doi:10.1111/j.1556-4029.2011.01793.x. ISSN   1556-4029. PMID   21554307. S2CID   14357171.
  28. Kang, Dake (6 November 2018). "Chinese 'gait recognition' tech IDs people by how they walk". Associated Press. Retrieved 15 June 2020.
  29. Chinese tech can recognise your walk , retrieved 27 December 2021

Further reading