title: Spinal Loads in Team Lifting
Creators: name: Dennis, Gary
Publisher: name: Griffith University
Year: 2003
Subjects: subject: spine
subject: lumbar spine
subject: spinal loads
subject: spinal injury
subject: lower back pain
subject: lifting
subject: team lifting
subject: load
subject: loads
subject: human mechanics

description: In the first experiment, spinal loads during individual and two-person team lifting tasks were compared. Ten healthy male subjects performed symmetrical individual lifts with a box mass of 15, 20 and 25 kg and symmetrical two-person team lifts with 30, 40 and 50 kg from the floor to standing knuckle height. Results indicated that the torque and compression force experienced by the lumbar spine were approximately 20% lower during team lifts compared to the load-matched individual lifting tasks. The two main and equal contributing factors reducing spinal load during team compared to individual lifting tasks were: (i) the increased horizontal pulling force and (ii) the ability of the team to hold the load at the ends of the box, which reduced the moment arm of the load. The second experiment assessed the effect of relative team member height (matched versus unmatched) on lumbar spinal loads during two-person team lifting tasks. Twelve young healthy male subjects performed matched and unmatched team lifts with two box masses (30 and 60 kg) and three initial box heights (0, 20 and 40 cm). Matched team members had standing heights within 5%, whilst unmatched teams had an average standing height difference of 25 ± 2.5 cm. Although spinal loads were reduced for the shorter subjects and increased for the taller subjects at the end of the lift, no significant difference was found in the maximum spinal loads incurred during matched compared to unmatched lifting conditions. In the final experiment the relationship between load mass distribution and the relative spinal loads incurred by each of the individual team members during two-person team lifting tasks was examined. Two-person lifting teams were required to lift a box containing a mass of 30 kg or 60 kg from the floor to standing knuckle height. Adjusting the position of the centre of mass within the box by ± 15 cm and ± 7.5 cm relative to the evenly distributed position (0 cm) yielded three load mass distribution ratios (69:31, 59:41 and 50:50), which represented the percentage of the total mass lifted by each team member. Although the spinal load incurred by the team member lifting at the heavier end of the load was greater than for the person at the lighter end of the load, the difference between the spinal loads incurred by each team member was not as great as the difference in the asymmetric distribution of the load mass. Subsequent investigation of the factors influencing spinal load indicated that the spinal loads experienced by the team member at the heavier end of the load was less than expected because they generated a larger horizontal pulling force than their lifting partner. Consequently, during the lift the load translated toward the team member at the heavier end of the load, which combined with the larger horizontal pulling force reduced the extensor torque required at the lumbar spine. Overall, results from this study have demonstrated that: (i) the lifting strategy used by two-person teams is distinguished from individual lifts by a greater use of horizontal pulling forces applied to the load and a decreased distance between the load and the lumbar spine, (ii) both the horizontal pulling force and the position of the hands on the load in team lifting have a load relieving effect on the lumbar spine and (iii) two-person team lifts performed by team members of unmatched standing height and with asymmetrical load mass appear to be coordinated in a manner that partially mitigates the increased spinal loads for the team member at increased risk of spinal injury.