Abstract
There are many industrial activities and work situations where heavy, but delicate pieces of equipment must be either handled, manipulated or placed into limited inlet spaces. Yet the accuracy of gross loaded motor performance and the levels of physical stress induced had not been methodically researched and was therefore investigated in this set of studies. Initially, the levels of truncal stress during the placement and removal of loads to and from a pigeonhole matrix were determined, which showed that truncal stresses were lower when handling to and from the central area of the matrix and increased significantly when handling loads to and from those boxes around the periphery. The variations in performance as well as truncal stress when handling to and from a pigeonhole matrix were examined in the next section of the work. The results confirmed the previous findings regarding truncal stress variation dependent upon position in the matrix, and also showed that there were significantly fewer placement contact errors in, the central area of the matrix than at the periphery. The placement of the load to the areas of the matrix which resulting in high truncal stress were observed to require the subject to adopt postures which involved shoulder rotation and/or lateral flexion, whilst only changes in truncal inclination and lumbar angle were made when placing loads to the lower stress areas. The effect of reducing inlet clearance between the load and the target box was found to reduce the level of performance, increase task duration, increase overall truncal stress, increase the post task heart rate and reduce both the peak and mean acceleration and the peak and mean force applied to the load. An inlet clearance of 10 cms was found be to critical for task performance. As the load size increased, the level of performance decreased even though the load weight was constant. Lifting and placing rectangular loads with their long axis orientated horizontally was found to result in better performance than when their long axis was orientated vertically. Fitts' index of difficulty postulated for psychomotor tasks has been shown to be applicable to gross loaded motor activities as well.