The subject in this study was a twenty year old female that was 1.68 meters tall and weighed 511.52 N. She was in good physical shape and had no musculoskeletal constraints. She was an able-bodied person using crutches. During the experiment she walked without contacting her left leg with the ground. The subject wore a black spandex "Cat Suit" with white Nike (c) tennis shoes. The subject had moderate experience with the Standard crutches, but had no previous experience with the Hope crutches. However, the subject practiced adequately (ten practice trials) with both sets of crutches before performing the actual trial runs. There were a total of seven markers used; six positioned on the subject and one put at the foot of each set of crutches. The six markers on the body of the subject were placed at: the acromion process of the shoulder, the lateral epicondyle of the elbow, the styloid process of the wrist, the greater trochanter of the hip, the lateral epicondyle of the knee, and the lateral malleolus of the ankle.
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Figure 1. Joint markers in the Hope crutch gait (left) and the Standard crutch gait (right). For both movements, joint markers were placed at the acromion process of the shoulder, the lateral epicondyle of the elbow, the styloid process of the wrist, the greater trochanter of the hip, the lateral epicondyle of the knee, the lateral malleolus of the ankle, and the foot of the actual crutch.
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The camera used for taping was a JVC Compact VHS camcorder video recorder model number GR-AX900/AX800. The video frame rate was 30 frames per second. Both sets of crutch gait recordings were done in a racquetball court in the basement of the Central Campus Recreation Building at the University of Michigan in Ann Arbor. The lighting within this location was standard gymnasium lighting and the camera was placed 5.15 meters away from the center of the gait-path line segment made by our two reference markers (one line of tape for each reference marker). The subject was instructed to move from one reference marker to the next using the crutches at a slow, natural pace with her right foot as the plantar foot. She began with the back of her right heel at the first reference marker and then was finished when any part of her right foot crossed the other reference marker. Three experimental trials per set were completed by the subject and recorded by the video recorder. In selecting the two actual trials for the comparative analysis, we analyzed both sets of trials and looked for the two that we felt exhibited the smoothest and most fluid movement.
The actual procedure for digitizing the video-recorded movements were as follows: the videotaped images were digitized at 30 frames per second using FusionRecorder on the Macintosh computers within the New Media Center at the University of Michigan in Ann Arbor. The digital video files were trimmed using MoviePlayer so that the data files contained only the frames between the start and end of the movements. Thus for each trial, the only footage that was used for analysis was the completion of one crutch-gait cycle (from heel strike to heel strike). A custom utility (QT-> PICT) was used to convert the Quicktime movie files into a series of individual frame files in PICT format for use with the Motion Plus software. The following markers: the acromion process of the shoulder, the lateral epicondyle of the elbow, the styloid process of the wrist, the greater trochanter of the hip, the lateral epicondyle of the knee, the lateral malleolus of the ankle, and the foot of the crutch were digitized using Motion Capture. Joint marker coordinate data were exported in spreadsheet format to Microsoft Excel (c) for biomechanical analysis using Motion Analyse.
