Temporal relationships of load and lumbar spine kinematics during lifting

Abstract

Most industrial lifting guidelines assume that lifts are executed in a slow and smooth manner. However, these guidelines are not consistent with empirical observations made in industry. Although many researchers have identified the importance of kinetic and kinematic variables to the understanding of low back pathomechanics, few have investigated the temporal relationships between the dynamic inertial characteristics of the load and the kinematic profiles of the lumbar spine. Five subjects were instructed to lift a 0.035 m 3 box from an initial starting height of 0.45 m to standing knuckle height. Six lifts ranging from 6% to 66% of the subject's mass were collected. Subjects were instructed to complete each lift in the sagittal plane, although no attempt was made to limit movement outside this plane. A V-scope ultrasonic monitor (Litek Advanced Systems, Rosedale, CA, USA) was used to determine the vertical kinematics of the load for each lifting condition. A lumbar motion monitor (Chattanooga Group, Hixson, TN, USA) was used to determine the flexion–extension kinematics of the lumbar spine for each lifting condition. Results revealed that changes in load kinematics were not consistent with changes in lumbar kinematics, particularly in the acceleration profiles. Relevence to industry Lifting guidelines typically recommend a smooth lifting technique in order to minimize the risk of occupational injury. However, the inertial forces of the trunk play an important role in the development of load momentum. Thus, temporal events, such as vertical load and back extension accelerations, must be better understood in order to determine safe lifting limits.