Factors affecting seat contour characteristics

This project focused on identifying the influence of subject characteristics and foam properties on seat contours in order to explain the load transfer between the buttocks and cushion. Seat contours were recorded for 17 people (11 spinal cord injured and six able-bodied individuals). Contour characteristics were represented by maximum contour depth, surface area, and displaced volume. Subject characteristics were represented as intertrochanteric distance, body weight, and lower extremity muscle tone. Two foams with different degrees of stiffness (45- and 55-pound indentation load deflection [ILD]) were studied. Multiple regression equations were calculated for each of the three contour characteristics by entering in all three subject attributes. While the equations differ, all six exhibited a significant Multiple R (range: 0.79 to 0.92). Each subject characteristic was a significant predictor of at least one contour trait (p less than 0.05). The major difference between the two cushions was the predictive ability of muscle tone. For the stiffer HR55 foam, muscle tone was the strongest predictor of all contour characteristics. Therefore, some conclusions can be drawn concerning the relationship between foam stiffness, tone, and resulting seat contours. These relationships help define the differences in load transfer as subject and cushion characteristics vary and are important in the design of contoured foam for use as wheelchair cushions.