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Application of Multimedia To The Study of Human Movement

Chris Kirtley

Dept. of Rehabilitation Sciences, The Hong Kong Polytechnic University, People's Republic of China


Ray Smith

School of Physiotherapy, Curtin University of Technology



A comprehensive package for studying human movement is presented. The combination of QuickTime digital video and graphs plotted on selection of the appropriate biomechanical tool is used to provide an intuitive learning interface, with muscles being drawn directly onto the video to further enhance realism. The data can be generated internally in the package with the addition of a simple inexpensive video camera, or imported from a variety of biomechancal equipment. It has been in use for some two years, with enthusiastic feedback from students, and has prompted the creation of a web-site and email list for discussion of patient cases.


Physiotherapy is currently an upwardly moving discipline, having recently been moved from the hospital to the university environment. A large and growing gap now exists between the theoretical basis of movement as revealed by computerised three-dimensional biomechanical motion analysis and the traditional empirical understanding and treatment of movement disorders (Kirtley, 1995). The teaching of human movement is a fundamental part of the education of a physiotherapist, but has been limited to a somewhat basic and didactic approach using traditional educational technology. By its very nature, the subject does not lend itself to a static representation on the printed page (Kirtley & Smith 1996a).

Digital video, with its ability to be simultaneously delivered to many users, is a long awaited solution. Since it can be controlled by each individual student, on standard computers with no special hardware, it offers a much greater potential than video tape. Moreover, the digital format facilitates the superimposition of information in a graphical format, to link abstract concepts with the real world (Kirtley & Phillips, 1996). A package has been developed to exploit this potential, which provides such control, facilitating a much deeper understanding of human movement (Kirtley & Smith 1996b).


A combination of QuickTime video of the movement with graphs of key biomechanical variables was used, with a cursor being used to control the video whilst indicating the corresponding point on the graph. Scripting was done in the SuperCard authoring environment, and a toolbox analogy was used to select the graph to be plotted. This was not straightforward, since QuickTime movies include many double frames, so a separate external function had to be written in C.


Fig. 1: Analysing mode, in which biomechanical tools are used to study the motion. From left to right and top to bottom, they are: angle (selected here), ground reaction forces, centre of foot pressure, height, joint moment, mechanical power, power flow (dimmed here because it is unavailable - a segment rather than a joint needs to be selected), work (also unavailable), velocity, acceleration, joint compressive force, muscle activity, normal range (selected here), left-right (shows data for the contralateral side), help, electromyography, trash (erases all graphs), audio help (gives short prompts to tell the student what to do next), camera (takes a snap-shot of the screen), and off button. Note also the side and joint selector above the toolbox. The active muscles (in green or red accoriding to their function) and ground reaction vector have been automatically drawn from moment, power and force data.

Icons were deliberately used throughout to simplify navigation and encourage interaction: very often in biomechanics, the introduction of mathematical formulae provokes a negative emotional reaction. By clicking on the help button whenever a tool is selected, a small tutorial can be obtained on the relevant biomechanical variable.

A unique feature of Motion Toolbox is the facility for drawing the active muscles directly onto the digital video (fig. 1). These are generated from joint moment and power data: the joint moment indicates which muscle is currently contracting, while the joint power indicates the magnitude of the contraction, and whether the muscle is acting concentrically (doing external work) or eccentrically (braking the joint). This enables the muscle to be drawn at the appropriate place on the body with a size indicative of the magnitude of the contraction and colour (green or red) representing the type of contraction (concentric or eccentric). Similarly, the size and direction of the ground reaction force on the foot can be superimposed. In this way, these quite complex abstract concepts are directly linked to the real world for intuitive understanding.

Data can be input from a variety of sources, and the architecture was deliberately kept open, with each biomechanical variable being stored in a simple ASCII text file, filed in the appropriate folder (e.g. Joe Bloggs:Right:Sagittal:Hip:Moment). This also enables the program to very quickly check which tools are available to avoid giving the student a choice of something which doesnít exist. There are potentially hundreds of variables possible for a given motion, and they may be measured by a several different pieces of equipment, e.g. motion analysis systems, force platforms, electromyography, foot pressure measurement systems (Kirtley & Kranzl, 1997), and each may operate at a different sampling rate. An open architecture is thus needed to allow maximum possible flexibility.

Fig. 2: Digitising mode, in which the student tracks markers on the joints to measure the kinematics. The stick figures show previously digitised frames of the video. Joint angles and segment lengths are shown on the bottom left. Once digitised, pressing the joint angle button will filter the data and calculate all the kinematics of the motion. The force platform icon is used to process ground reaction force data from a supplied text file (this data is often recorded on a separate data acquisition system, often on an IBM-PC compatible). Once this is done the lamp icon will become available, allowing the student to calculate the joint moments and powers by inverse dynamics modelling. If electromyography (electrical signals recorded from the muscles) has been collected, it can also be imported by clicking the electrical plug icon.

One way of generating data is to use Motion Toolbox itself. By connecting an ordinary domestic camcorder, video can be recorded directly to the computer and analysed by the package (fig. 2). This is a useful educational tool, since it provides the student with a hands-on means of getting involved in the process of biomechanical analysis, which is considered essential if a deep understanding of the concepts is to be achieved. The student has to identify anatomical landmarks in each frame of the video (there would be typically about twenty in an average stride of gait), and these co-ordinates (after low-pass filtering to eliminate noise) are then used by the package to compute the joint angles, velocities and accelerations by digital signal processing. Each stage of the process is clearly shown as the calculations proceed, so that the student can follow the steps involved. An automatic tracking algorithm is also included for use when reflective markers are attached to the subject. The co-ordinates are also used by the package when superimposing the active muscles onto the video.


Feedback from students using the package has been uniformly enthusiastic, and it is now providing the basis for several student projects in Perth and Hong Kong. Typically, the students suggest a topic for analysis, such as the effect of wearing platform-soled shoes, or carrying a large load on walking mechanics. An added bonus is the ease with which the cases can be uploaded to the World Wide Web, and a Clinical Gait Analysis site ( & email list ( for the study of gait disorders now has over 400 subscribers world-wide. These subscribers include students, doctors, therapists and bio-engineers who get together in a virtual ìgrand roundî to discuss cases presented on the web-site. So far, some 24 cases have been discussed in this way.

A lecturer in physical therapy at Northeastern University in Boston, USA, Dr. Jan Bruckner, has successfully used some of the cases recorded to teach Movement Science to her undergraduate students, who were each assigned a case on which they were asked to write an appraisal. After favourable feedback from the students, a JavaScript applet was developed ( which provides a study interface, comprising the digital video and motion analysis results, multiple choice questions and feedback on the studentís performance. This is currently being developed further to allow the curves to be plotted in response to the studentsí button presses (as in Motion Toolbox), which will be tracked and used to analyse their problem-solving processes.

Yet another use for the package is internet-based telematics. The ease of sending digital video over the internet has allowed a motion analysis service to be provided to a hospital in Vienna, Austria, which would otherwise be isolated from the services of a motion analysis laboratory.


Kirtley C (1995) Multimedia: A Paradigm Shift In The Teaching Of The Biomechanics Of Human Movement. Teaching & Learning: a focus on learning, Edith Cowan University, Perth, Feb. 7-9, 1995.

Kirtley, C., Phillips, R. A. (1996). Movement Toolbox: An Interactive Multimedia Package for Studying Human Movement. Proc. 3rd International Interactive Multimedia Symposium, Perth, Western Australia, 197-202.

Kirtley C & Smith RA (1996a)Movement Toolbox: a multimedia package for movement analysis, Proc. 1st Australian Biomechanics Conference, Sydney 1-2 Feb. 2-3.

Kirtley C & Smith RA (1996b)Motion Toolbox: an interactive multimedia package for studying human movement. Proc. of the Annual. Conf. of Higher Education Development Society of Australia (HERDSA), Perth, Australia.

Kirtley C & Smith RA (1997) Multimedia Applications And Tools (in press, ref. MTAP 110-97)

Kirtley C & Kranzl A (1997) New Diagnostic Technology in Rehabilitation: computerised gait analysis offers multimedia possibilities. Rehab Management International, 7 (1): 60-62.


(c) Chris Kirtley, Ray Smith


The author(s) assign to ASCILITE and educational and non-profit institutions a non-exclusive licence to use this document for personal use and in courses of instruction provided that the article is used in full and this copyright statement is reproduced. The author(s) also grant a non-exclusive licence to ASCILITE to publish this document in full on the World Wide Web and on CD-ROM and in printed form with the ASCILITE 97 conference papers, and for the documents to be published on mirrors on the World Wide Web. Any other usage is prohibited without the express permission of the authors.

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