Manual handling in non-inertial reference frames

BACKGROUND: This paper reports on the torques developed in the shoulder joint experienced by occupants of moving vehicles during manual handling tasks. Handling heavy weights can cause musculoskeletal injuries, especially if handling is done with arms extended or at high levels.
OBJECTIVE: The aim of the study was to measure the longitudinal and lateral accelerations in a variety of passenger vehicles together with the postures of subjects lifting luggage onto store shelves. This data enabled the application of inverse dynamics methods in a non-inertial reference frame to calculate the shoulder joint torques.
METHODS: The subjects lifted 3 pieces of luggage of masses of 5kg, 10kg and 14kg onto shelving which was at heights of 1.2m, 1.6m and 1.8m. The movement of subjects was measured using a 12 camera, 3-dimensional optical tracking system. The subjects stood on force plates to measure the ground reaction forces.
RESULTS: 63 trials were completed, although 9 trials were aborted due to the subjects feeling unable to complete the task. It was found that the shoulder torques exceeded the levels recommended by the UK Health and Safety Executive for manual handling. A lift assistance device is suggested to reduce the shoulder torques required for luggage handling.