Neuromuscular and coordination changes related to a prolonged asymmetrical lifting task

Thumbnail Image



Journal Title

Journal ISSN

Volume Title


University of New Brunswick


According to epidemiological research, industrial lifting has been highly correlated with musculoskeletal disorders (such as low back and shoulder pain) (Danneels, 2001) However, the sources of what trigger the discomfort/pain are not conclusive (Wilson, S 2003). Twenty-one female participants performed an asymmetrical lifting task at a rate of 6 lifts per minute for seventy-five minutes. The lift envelope was from the floor to a shelf at waist height set 60 degrees to the right hand side of the starting position with a handled box weighing 10% of participants' predetermined maximum lifting capacity. Electromagnetic motion tracking sensors were attached to the participant's hands, arms and back to measure lifting kinematics. A static calibration was used to establish relationships between each marker and corresponding anatomical landmarks. EMG sensors were placed on the skin over the Trapezius, Anterior Deltoid, Spinae (T10), and Latissimus dorsi to measure neuromuscular activity of targeted muscles. A static hold of a ten pound weight was used before and after the lifting task to measure if participants fatigued. After the asymmetrical lifting task the participants showed strong indications of fatigue (RPE scores increased and MVC scores decreased). Also, the MPF & RMS quadrant indicated that the majority of participants experienced fatigue in the left and right upper trapezius and latissimus dorsi (TlO). Kinematics significantly altered over time. A significant increase in ROM was found during the lifting task in the right shoulder adduction/abduction and rotation. During lowering tasks, a significant increase in ROM was found on the right shoulder flexion/extension, rotation and trunk flexion/extension. Such specific kinematic anatomical alteration for female lifters is a cause for concern for developing lower back pain (LBP) due to acute herniation of the intervertebral disk, which is commonly seen in repetitive lifters (Kingma et al., 1998) and shoulder MSDS (Bjelle et al., 1979).