Change in twisted trunk postures by the use of saddle seats - a conceptualstudy

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 ne ed for an ergonomic tool that can easily be mounted on existing tractors. T his investigation was initiated as one link towards such a tool. The purpos e was to study whether the exposure to twisted trunk posture decreased when driving an agricultural tractor in the field using freely swivelling saddl e chairs. Ten subjects employed as tractor drivers volunteered for the stud y. They were video recorded from above during harrowing and ploughing sitti ng 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-should er angle and these intervals were then classified into three exposure level s. An exposure variation analysis was carried out for each driver within ea ch work operation. The results showed that the exposure to extreme twisted trunk postures was slightly reduced during harrowing using a saddle chair c ompared to the conventional chair. When ploughing, the amount of drivers wh o 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 particul ar advantage during highly static work operations, with a small amount of l ow-frequency vibration load on the driver. (C) 2001 Silsoe Research Institu te.