Measuring Human Movement

Cooch Memorial Lecture, The Barn, Field Place, Worthing. Tuesday 8thNovember Measuring Human Movement by Prof Mike Whittle
Mike started by reviewing the history of the investigating human movement (or gait analysis). The pioneers of scientific gait analysis were Aristotle and much later in 1680 Giovanni Alfonso Borelli. In the 1890s, the German anatomists 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, it became possible to capture image sequences which reveal details of human and animal locomotion that are not noticeable by watching the movement with the naked eye. Eadweard Muybridge and Étienne-Jules Marey were pioneers of this in the early 1900s. It was photography which first revealed the detailed sequence of the horse “gallop” gait, which was usually mis-represented in paintings prior to this.
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 which 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 which are routinely used in large numbers of cases, both 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 Vicon Motion Systems and BTS, marketing gait analysis hardware systems in the mid-1980s.
Mike than described how modern gait analysis is undertaken. Medically, this is to aid in understanding gait abnormalities and in treatment decision-making This commonly involves the measurement of the movement of the body in space (kinematics) and the forces involved in producing these movements (kinetics) using a variety of systems and methodologies.
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.
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. 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 – wwhich cannot be seen and therefore does not distract the patient) with matching filters to record the reflection from the markers placed on the body. Markers are located at 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.
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 Inertial (cameraless) systems based on 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.
A typical modern gait lab has several to many cameras (video and/or infrared) placed around a walkway or treadmill, which are linked to a computer. The patient has single markers applied to anatomical landmarks, or clusters of markers applied to the middle of body segments. The patient walks down the walkway or the treadmill and the computer calculates the trajectory of each marker in three dimensions. A model is applied to compute the underlying motion of the bones. This gives a full breakdown of the motion at each joint.
In addition, to calculate movement kinetics, most laboratories have floor-mounted load transducers, also known as force platforms, which measure the ground reaction forces and moments, including magnitude, direction, and location (called centre of pressure).
To conclude his talk Mike briefly described some other applications of gait analysis. The entertainment industry (mainly computer gaming and motion pictures) is now a major user with highly complicated systems using many cameras. Gait analysis is also used in scientific research, ergonomics, police investigations and sports training and umpiring.
There followed a lively question and answer session.
R Keir