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The motions studied In biomechanics today are Increasingly more complex, requiring spatial, force and myographic measures. The Peak system employs off-the-shelf video equipment and an AT compatible microcomputer to perform spatial and analog data acquisition. Every video field can be analyzed in either NTSC (North American) or PAL (European) video formats. Video sampling rates can vary from 50 to 2000Hz, depending upon the video hardware used. The body locations of interest may be obtained using any of three methods. The manual acquisition method superimposes a colored cursor over the video image and its position is controlled by a handheld mouse. The semi-automatic option controls the initial position of the cursor by predicting the position based upon its location in previous frames. The value of these options is that they can be applied in difficult experimental settings or for digitizing points that are internal to the body (e.g., joint centers). The third method is automatic tracking, which determines the center of area of a marker that contrasts with its immediate background. An individual criterion may be set for each marker to discriminate it from noise, background and other markers. Hidden markers can be treated via manual digitization, interpolation or ignored if seen by other cameras. Once collected, spatial data can be translated and/or rotated with respect to external reference frames, or to internal reference frames within the moving subject. An analog to digital sampling module acquires data from sensors and synchronizes them with the video generated spatial data. Subsequently, complete motion information can be generated rapidly and accurately for countless applications. The performance of the video measurement system was assessed by measuring its precision and accuracy in two dimensional static tests. The precision for manual digitizing was found to be 1 in 2422 and for automatic digitizing, 1 in 5280. The accuracy for manual digitizing was found to be 1 in 3267 and for automatic digitizing, I in 4310.
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