The Effects of Load Stability and Visual Access During Asymmetric Lifting Tasks on Back and Upper Extremity Biomechanical Responses

To explore the change of muscular and biomechanical responses in different load stability and visual access conditions during an asymmetric lifting task. Previous studies found that lifting unstable loads resulted in changes to the biomechanical loads experienced by the spine and upper extremities. However, researchers have not extensively investigated behaviors when people lift potentially unstable loads. It was hypothesized that lifting a potentially unstable load can lead to changes in lifting behavior, which may be mitigated by visual access to the load. Fourteen volunteers lifted either a stable load or a potentially unstable load that could move within the container during the lifting task. In half of the lifting conditions, the box was covered to restrict visual access when lifting. Spine kinematic and kinetic measures and surface electromyographic (EMG) signals from back, shoulder, and arm muscles were obtained. Lifts of the stable load were faster and generally had higher peak muscle activations than lifts of the potentially unstable load. Participants had less spine flexion when handling the potentially unstable load without visual access. When lifting and moving a potentially unstable load that could lead to a perturbation, people tended to lift the container more slowly comparing with lifting a stable load, which in turn reduced the peak muscle activities. In industry, there are many work situations where workers need to lift or carry unstable loads that can shift during transport. Providing visual access to the load may help mitigate some of these effects