Sit-to-Stand Movement Pattern A Kinematic Study - Physical Therapy

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Fig. 1. Angles between body segments: the ankle (Angle 1), the knee (Angle 2), and the hip (Angle 3). the subject. An electronic digital timer visible in the photographic field provided accurate time measurement. The camera was operated at a film speed of 32 Frames per second. Additional details of the filming method are described in a previous report. 8 Procedure Data points were established over the following body landmarks: the fifth metatarsal head, lateral malleolus, lateral femoral epicondyle, greater trochanter, midiliac crest, acromion process, tragus, and the mid-Frankfort plane. (The Frankfort plane, the center of which approximates the head's center of gravity, is located between the tragus and the lowest point of the orbit.) These data points defined the angles of interest of our study (Figs. 1,2). The data points on the fifth metatarsal head, the lateral malleolus, and the lateral femoral epicondyle were used to measure the angle of the ankle joint (Angle 1). The lateral malleolus was located at the vertex of this angle. The lateral malleolus, the lateral femoral epicondyle, and the greater trochanter defined the knee angle (Angle 2), with the lateral femoral epicondyle at the vertex. The hip angle (Angle 3) was Fig. 2. Angles of inclination: the pelvis (Angle 4), the trunk (Angle 5), the neck (Angle 6), and the Frankfort plane (Angle 7). defined by the lateral femoral epicondyle, the greater trochanter, and the midiliac crest. The greater trochanter was the vertex of this angle. Figure 1 identifies these angles. The angular values we recorded reflect the relationships among the body landmarks identified by the data points (Table). These landmarks, however, are not always analogous to the clinical measurements. For example, because of the increased objectivity permitted by photographic measurement and data reduction, the data points of the ankle angle were not analogous to the bony landmarks used by the clinician to obtain goniometric measurements. Our ankle values, therefore, reflect a greater degree of plantar flexion than would be recorded by clinical measurement. In addition to these three lower extremity angles, we also were interested in the movements of other body segments. These body segments, defined by a line connecting two data points, were 1) the pelvis, between the greater trochanter and the midiliac crest; 2) the trunk, between the midiliac crest and the acromion; 3) the neck, between the acromion and the mid-Frankfort plane; and 4) the Frankfort plane, between the mid-Frankfort plane and the tragus. The relationship of each body segment to the horizontal plane was computed, and 1710 PHYSICAL THERAPY Downloaded from http://ptjournal.apta.org/ by guest on June 15, 2013
these angles are referred to in this article as the angles of inclination (Fig. 2). The trunk and neck angles of inclination also are relative and should not be construed as the true reflection of trunk or neck movement. First, the data point on the acromion is on the appendicular skeleton. Second, no attempt was made to assess specific spinal mobility. The subjects were asked to assume a seated position of readiness. Verbal commands were standardized: "I want you to get ready to stand up. Scoot as far forward in the chair and bring your feet as far back as you need to stand up comfortably. Rest your hands lightly on your thighs but do not push with them when you stand up. Do not stand up until you hear me say, 'Stand.'" No further attempts were made to control the subjects' postural set. After three to five trial movements, we filmed the subjects as they stood up from a sitting position in their usual manner and at their usual speed. Three consecutive trials for each subject were recorded on film. One trial from each subject was selected for analysis. The criteria for trial selection, in order of their importance, were 1) ability to view all data points on each frame, 2) subjective appearance of the movement as smooth and natural, 3) feet flat at the beginning of the movement, 4) feet symmetrical at the beginning of the movement, and 5) a clearly defined completion of motion. The frame preceding the first discernible body movement was the first to be reduced. If the subject exhibited postural sway, the end of motion was represented by that frame in which no further forward displacement of the pelvis occurred. Data were reduced from each frame up to, and including, this last frame. Data Reduction An electronic graphics calculator ‡ was used to place the projected film image in a two-dimensional, Cartesian-coordinate system and to assign each data point x and y spatial coordinates. The calculator was interfaced with a Texas Instruments Silent 700 ASR § electronic data terminal, which recorded x and y coordinates on digital magnetic tape cassettes. Data from these tapes were transferred later to magnetic disks and made accessible to a Xerox Sigma 6" computer. A FORTRAN IV computer program was written to reduce the data and allow for additional analyses. Computations were made to correct for equipment error and to compensate for the distortion inherent in the data. Angles between body segments (Fig. 1) were calculated using the dot product method. 9 As noted earlier, because these values reflect the relationships among body segments, they are not always analogous to clinical measurements. For example, in this study, both knee and hip extension approached 180 degrees, not 0 degrees. Numerical values for angles of inclination of the pelvis, trunk, neck, and Frankfort plane (Fig. 2) were computed with respect to the horizontal x axis. The positive x axis, the reference line, was 0 degrees; the positive y axis was 90 degrees with respect to the horizontal axis. Positive angular values reflected angular deviations occurring in a counterclockwise direction from the positive x axis. Negative angular values ‡ Numonics Corp, 418 Pierce St, Lansdale, PA 19446. § Texas Instruments, Inc, Houston, TX 77011. 1 Xerox Corp, El Segundo, CA 90265. RESEARCH Fig. 3. Left diagram depicts a representative movement pattern. Data points are joined by lines to form 21 stick figures (sampling rate), Enhanced line on the left indicates the initial position; the enhanced line on the right indicates the final position. Right diagram depicts trajectories of data points at the tragus, acromion, midiliac crest, hip, and knee. reflected angular deviations occurring in a clockwise direction from the positive x axis (ie, below the horizontal axis). Data Analysis For intersubject comparison, the movement time of each subject was divided into 5% increments. This division, which included the initial starting position, provided for 21 points of comparison within the movement. For each 5% interval, the mean and standard deviation of each angle were calculated across all subjects. The mean horizontal and vertical coordinates of each data point were used to construct a model of the starting position and a schematic diagram of the entire movement cycle (Fig. 3, left diagram). Average x and y coordinate values also were used to graph trajectories of body landmarks during the movement cycle (Fig. 3, right diagram). RESULTS Movement time ranged from 1.3 to 2.5 seconds. The average movement time was 1.8 ± 0.3 seconds. Pattern of Movement Figure 3 (left diagram) illustrates the data from the Table in graphic form. The initial position of the representative movement pattern is indicated by the enhanced line on the left; the final position is indicated by the enhanced line on the right. When the model stick figure leaned forward, the trunk inclined to an angle of 80 degrees counterclockwise Volume 66 / Number 11, November 1986 1711 Downloaded from http://ptjournal.apta.org/ by guest on June 15, 2013
Page 1 and 2: Sit-to-Stand Movement Pattern : A K
Page 3: TABLE Mean Angular Positions Comput
Page 7 and 8: In Burdett et al's comparison of ri

Sit-to-Stand Movement Pattern A Kinematic Study - Physical Therapy

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