Pressure variation under the ischial tuberosity during a push cycle.

The present study is devoted to the variation of the magnitude of the compressive loading acting on the soft seating parts of a disabled person and the related pressure distribution under the ischial tuberosity during wheelchair propulsion. A combined experimental and computational approach was designed to predict correctly the change in magnitude of the maximum internal shear and compressive stresses produced by different propulsion speeds, cushion characteristics and body position of the subject. The results obtained show that the vertical force acting on the seating parts increases with the propulsion speed and exceeds the body weight by more than 100%. The related pressure under the ischial tuberosity shows a significant increase of 125% on the tissue/seat interface and an estimated increase of 185% in the peak compressive stress. It is concluded that computer modelling using a quasi-static approach provides a reliable estimate of the pressure values by the observed loading frequencies of 0-4 Hz. It can also be noted that the time independent material model utilised for the bulky soft tissue proved adequate for the estimate of the pressure level occurring under the ischial tuberosity during a push cycle.