Figure 1. Joint markers in the squat lift (left) and the stoop lift (right). Joint markers were located on the load, shoulder, hip, knee, and ankle.
The subject for this study was a 21 year old male, who is 1.8034 m tall and has a weight of 823N (185 lbs). The subject wore a bathing suit, socks and athletic shoes. Clothes were kept at a minimum so that the movement of the subject was recorded, not the movement of his clothes. The subject has no previous experience lifting boxes of these types, although it should be noted that he lifted weights on a regular basis. Joint markers were placed on the subjects body at the greater trochanter (hip), acromion process (shoulder), lateral epicondyle (knee), and lateral malleolus (ankle). A marker was also placed on the subjects hands, at the spot where the center of the handles would be when he lifted the box. The markers will be of the "pinwheel" fashion, painted black and white, so as to show up well when digitized.
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Figure 1. Joint markers in the squat lift (left) and the stoop lift (right). Joint markers were located on the load, shoulder, hip, knee, and ankle. | |
The subject lifted a box weighing 155.7 N (35 lbs). The subject was told to lift the box first by squatting, and then by stooping. The experimenters showed the subject how to lift before taping began. Lifting techniques were videotaped on the parking deck between University Health Services and the Power Center at the University of Michigan. The backdrop seen is the back of the Power Center. The videotaping was done using a Sony Hi-8 camcorder placed approximately 3 m from the subject. The frame rate of video recording was 30 frames per second (fps). Only natural light was used during recording. Reference markers (orange bottles) were placed approximately 2.2 m apart, and the subject was situated between them. One trial consisted of a leg lift followed by a stoop lift. The subject performed five trials, with only the final four considered to be the best. After viewing the video cassette, trial number four was selected, because three of the other trials turned out to be of poor picture quality, and trial five was an inferior trial performance.
The videotapes were digitized at 30 fps using Fusion Recorder on Macintosh computers at the New Media Center at the University of Michigan. The digital files were trimmed using Movie Player so that the data files contained only frames between the start and end of the movements. A custom utility (QT->PICT) was used to convert the Quicktime movies into a series of individual frame files in the PICT format for us with the MotionPlus biomechanical software. Joint markers on the shoulders, hip, knee, ankle, and hand were digitized using Motion Capture. Joint marker coordinate data were exported in spreadsheet format to Motion Analyse for biomechanical analysis.