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Gideon B. Ariel, Ph.D.


Biomechanical instrumentation has made enormous progress during the last two decades. Prior to 1968, biomechanical processes were slow, tedious, and frequently contaminated with arithmetic error. Computerization of many of the steps significantly influenced the growth of biomechanical applications. One major improvement replaced the tedious paper, pens, and mirrors tracing technique occurred with the introduction of the first electronic digitizer with immediate application to Olympic athletes (1). The device not only decreased the time needed for locating and storing joint center coordinates, but reduced many of the tracing and measurement errors. In addition, the "digitizing" process was conducted at one location and the digitize points transferred on-line to the time sharing system on a main frame computer.(2).

The Internet has opened a new frontier for research and international cooperation on multifaceted studies. Although the restrictions due to geographical distance and time discrepancies pose some limitations, facilitating the acquisition of x, y coordinates could enhance cooperative research efforts. One technique for acquiring motion coordinates, that is, "digitizing" on the Internet, has been developed for the purpose of facilitating research inquiries.


The purpose of the present study was to test a newly developed technology for digitizing between remote sites using the Internet as the communication medium. In other words, the video sequences resided on one computer and the remote site was responsible for securing the x,y coordinates through on-line processing.

Golfers were filmed during a local club competition. All golfers performed the same golf drive at the same location which was selected for the test sequence. Two cameras were placed at approximately 45 degrees to the plane of the path of the golf swing and were camouflaged in a manner which would not distract the competitors. Following data acquisition of all the participants, one swing for two of the contestants were selected for analyses.

The video sequence was "grabbed" or "captured" using an field-by-field advance VCR. The video data was stored in AVI format on a computer located at Site A while the digitizing computer, Site B, resided at a distance of approximately 1500 km. The first step was determination which the specific portion of the golfers' swing was to be selected for subsequent analysis. Although the actual digital data was stored on the computer located at Site A, the researcher examined the video portion, field by field, on his screen at the remote site, Site B. The resolution at each site is determined by the is the size of the pixels at the digitized site. The researcher at Site B examined the specified sequence field-by-field by controlling the server computer and selected a sequence for analysis.

After determining the portion of the performance for analysis, the researcher had to define the joints to be digitized. Specialized instructions were presented for defining the specific joints, such as the foot, ankle, knee, hip, as well as the golf club and ball. Following several other steps for naming and labeling files, the actual digitization began. As each of the selected points were digitized, the x,y coordinates for that point were determined immediately and were stored on the server computer in the appropriate file. The digitized points, in concert with the Common Gait Interface (CGI), created a matrix of x,y, coordinates for further analysis. If only the two-dimensional analysis (2D) had been desired, the analytic portion would have been performed at this point. Since, 2 cameras had been used to record the event, it was possible to obtain the preferred three-dimensional (3D) analysis. Therefore, the digitization process was repeated for the second camera view.

Following the digitization procedures, the researcher had to establish an interface to the server using the a commercially available program, namely, the HTML version 3 of Netscape. For this study, an ISDN telephone line was used with a transmission speed of 128K bits per second. This type of communication line normally requires less than 2 seconds to download each image. Since not all digitizing sites would have ISDN capabilities, the same sequence was tested using a 28.8K modem. The transmission time required using the 28.8K bits per second modem was about 15 seconds per image. It was determined that the test sequence was a length which reasonably reflected a normal, acceptable time allocation for biomechanical researchers.


After establishing the interface with the server, the researcher at Site A transmitted each of the digitized view files from the server (Site B) to his own computer at Site A using the File Transfer Protocol (FTP) Internet function. The files were reconstructed at Site A to determine if the data had been transmitted accurately. The data was confirmed to be identical to the duplicate set which was stored at Site B.

The results demonstrated the use of the Internet to digitize kinematic data collected and maintained at one geographic location while the researcher was located at a second site.


The study successfully demonstrated that digitization is a biomechanical task which can be performed between different geographical locations using the Internet as the interfacing medium. The applications of this technique and intellectual resource appear unlimited.

For example, a golf teacher in New York can video his students' swings. These video clips can be transmitted digitally in AVI format to a server in one part of the world and then interfaced to the biomechanical program for further analysis. Many Olympic events make fixed laboratory studies difficult, such as equine, sailing, or distance skiing. Coaches can film actual performances on site using cameras with direct AVI format input attached to Laptop computers. These files can then be digitized or transmitted through Internet protocols.

Biomechanical quantification has developed far beyond the pioneers who relied upon visual observations of animation to describe movement. The revolution continued with improvements in cameras, the introduction of computers, development of various algorithms to better fit the data, and expansion beyond sports studies. The ability to quantify motion has appeal to many groups and at many different levels. Access to global resources via the Internet expands biomechanics beyond a fixed geographical location. Researchers and lay persons will be able to digitize from the computer in their home, laboratory, or on the airplane.


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