Change in Twisted Trunk Postures by the Use of Saddle Seats - a Conceptual Study

The seated, twisted trunk posture when driving an agricultural tractor is a risk factor for low-back pain. Beside new cab designs, there is still a need for an ergonomic tool that can easily be mounted on existing tractors. This investigation was initiated as one link towards such a tool. The purpose was to study whether the exposure to twisted trunk posture decreased when driving an agricultural tractor in the field using freely swivelling saddle chairs. Ten subjects employed as tractor drivers volunteered for the study. They were video recorded from above during harrowing and ploughing sitting on one conventional and three different types of saddle chair. The chair angles, chair-hip angles, hip-shoulder angles and time period lengths were determined for the different postures assumed when driving. The angles and time period lengths were classified into six intervals based on hip-shoulder angle and these intervals were then classified into three exposure levels. An exposure variation analysis was carried out for each driver within each work operation. The results showed that the exposure to extreme twisted trunk postures was slightly reduced during harrowing using a saddle chair compared to the conventional chair. When ploughing, the amount of drivers who were exposed to extreme twisted trunk postures during the runs across the field was reduced by some 50% with the use of saddle chairs. The use of a freely swivelling mechanism and enough space to swivel would be of particular advantage during highly static work operations, with a small amount of low-frequency vibration load on the driver.