Prolonged seating can cause musculo-skeletal problems in the long term if poor postures are adopted. A three dimensional static model of the body to calculate the intervertebral disc compression at the fifth lumbar disc was built. SAMMIE, a computer aided ergonomics package was used for modelling a computer operator workstation and determination of joint centre locations and joint angles in a seated posture. Experimentation was also performed to determine the body-mass distribution on the seat used. No significant difference between male and female body-mass distribution was found. The static model found postures with the seat pan and backrest reclined to predict the lowest disc compression. Postures in which the operator was bent forwards gave the highest disc loadings.