Evaluation of meat-hook handle shapes

Abstract

Seven meat hooks including two current designs and five new designs with flat-rectangular, frustum, double frustum, and cylindrical shapes were evaluated. A two-phase study was conducted. In the first experiment, maximum pulling forces were measured by load cell to evaluate the effects of handle shapes on subjective discomfort, maximum pulling force, and muscle activity. Two pulling forces, 15 and 30 kg, were employed to a pulley mechanism to simulate pulling a beef carcass horizontally in the second experiment. FSR (force sensitive resistor) glove was used to measure the pulling forces on the meat hooks. The glove has 12 sensors that result in placement on the pulpy regions of each phalange. In addition, a biomechanical hand model was developed and applied to predict tendon forces. Double frustum shaped handles produced significantly larger maximum pulling forces and best force efficiency when normalizing forces with EMG. In terms of external forces as measured by the FSRs, the averages of finger force contributions to the total finger force were 27%, 32%, 32%, and 10% in order from index finger to little finger. The averages of phalange force contributions to the total finger force were 20.9%, 33.7% and 45.4% for the distal, middle and proximal phalanges, respectively. A Chi-square analysis indicated that the phalange force distribution for double frustum handles deviated least from the average contributions for all hooks. Double frustum handles showed the least predicted tendon forces and normalized tendon forces per unit external force. The optimality of double frustum shaped handles was also supported by the lowest discomfort ratings. Therefore, based on both empirical physiological measurements and theoretical biomechanical calculations, a double frustum handle is most efficient for pulling task, producing the least amount of tendon forces. Relevance to Industry Results obtained from this handle study will help to reduce the ergonomic risk factors of finger/hand disorders for meat hook workers who use the meat hooks with a long daily duration and high force.