Trunk posture and trapezius muscle load while working in standing, supported-standing, and sitting positions

A study of standing, supported-standing ("riding" on a rounded seat), and sitting postures was carried out on persons simulating assembly work in places with poor leg space. These postures and the upper trapezius muscle load were examined using statometric and electromyographic methods, respectively. While supported-standing or sitting, the lumbar spine moved toward kyphosis, even where there was no backward rotation of the pelvis. In adopting the position for anteriorly placed work, the upper arms were raised 30 degrees forward or more; then, if a greater reach was necessary, the trunk was flexed as well. It is concluded that if leg space is poor, variation between supported-standing and standing should be encouraged, and an ordinary office chair avoided. Working level should be arranged so that it is lower than 5 cm above elbow level if no arm/wrist support is possible.