Safer Lifting at work

Warehouse workers often have to carry out physically demanding and repetitive tasks that lead to fatigue and put them at increased risk of injury, especially lower back pain. Most research on the impact of such jobs has primarily focused on the impact of constrained lifting tasks – but a new study has investigated how the body adapts to work-induced fatigue during a multiplanar lifting task.

The findings highlight the importance of considering ergonomics when designing tasks, to reduce the risk of injury. None of the participants had any previous acute or chronic back or shoulder injuries, or neurological or muscular disorders. Their session included maximal voluntary isometric contractions (MVICs) – tests to measure muscle strength – including maximal shoulder flexion, back extension, trunk flexion, trunk twisting and lateral bending bilaterally.

During a manual material handling (MMH) exercise, they were asked to lift, transfer and lower a mass (5kg for women, 7kg for men). The study suggests that as workers become fatigued, they alter their lifting technique to reduce the strain on their body.

The research notes: “The load moment arm decreased across the trial (4% decrease) and participants tended to complete movements faster (4% decrease). “Rectus abdominus [the top layer of the abdominal muscles] activity increased (4% MVIC increase), while anterior deltoid [front of the shoulder] activity decreased over time (20%).” This suggests the body engages core stability to compensate for fatigue in other muscles. A “potentially positive adaptation” noted during the trial was that participants decreased their hand-pelvis distance, which would result in “reduced acute and cumulative compressive forces on the lumbar spine”.

Some “potentially negative” adaptations observed included a “decrease in thorax-pelvis flexion deviation phase over time”. This indicates participants were repetitively loading the same tissues, increasing their risk of developing musculoskeletal disorders. The researchers concluded that participants “positively adapted to fatigue by decreasing the external moment arm of the load and by adjusting the relative amount of work vs. idle time, effectively resulting in reduced cumulative load to the lumbar spine”. They added that the findings could help “to optimise task design, as well as potential implications in injury risk”.