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. The complexity of an efficient human gait pattern becomes clear when it is compromised due to disease, trauma, or natural decline.
Clinical gait analysis is a proven scientific tool to identify impaired gait patterns (conditions affecting an individual’s ability to walk). The individual’s gait analysis is used to assess, plan, and treat the individual. Because of the time consuming, complex and thus expensive procedure, gait analysis is often only used for severe Cerebral Palsy and Stroke patients.
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 pattern.
Conventional gait analysis is generally executed in a large laboratory, average of 88m2 (947 ft2), and strictly limited to analysis based on an artificially targeted single step on the force-plate. 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. Traditionally, force-plates, electromyography (EMG), video cameras and a motion-capture system are used to collect gait parameters like walking-speed, step-size, joint angles, joint moments and muscle-activation.
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 market set, 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.
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 centre 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 (the Newton–Euler equations describe the combined translational and rotational dynamics of a rigid body. Traditionally the Newton–Euler equations describes the grouping together of Euler's two laws of motion for a rigid body into a single equation with 6 components, using column vectors and matrices) 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. This is why many labs also use surface electrodes attached to the skin to detect the electrical activity or electromyogram (EMG) of, for example, the 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.
Compiled by: Dr John Sandham CEng FIHEEM MIET