A kinematic, kinetic and electromyographic comparison of stooped sheep shearing techniques and shearing with a sheep manipulator

Traditional sheep shearing methods require workers to adopt postures where the trunk is approximately horizontal and held in that position against gravity for long periods of time. The objective of this study was to examine the biomechanics of stooped shearing techniques and to compare the effectiveness of a new sheep manipulator in reducing the frequency of these postures and the changes in low back forces and electromyographic (EMG) activity. Five male shearers were filmed using three video cameras and EMG and three-dimensional (3D) kinematic data were derived during seven segments of the shearing action. Kinematic data were used to calculate the L5/S1 compressive and shear forces using the 3D Static Strength Prediction Program(TM). Results showed the low back forces in stooped shearing were typically between 2200 and 3000N. Also, the sheep manipulator effectively allowed the shearers to maintain a more upright posture (mean trunk angle > 65degrees) which decreased the compressive (maximum < 1350 N) and shear (maximum < 260 N) forces at L5/S1. (C) 2004 Elsevier Ltd. All rights reserved.