What Is the Best Way to Lift?
Written By Linda Harley
 Number of nonfatal occupational injuries and illnesses involving days away from work in the poultry processing industry, as recorded by Hammock7. |
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In 1977, Duke Dubos1 asked the question: What is the best way to lift and carry? He identified the key elements needed to create an industry standard for safe lifting techniques. These elements formed the basis of what is known as the NIOSH lifting equation2, the standardized method for determining what the safe maximum weight is for an individual to lift. In a similar manner, the methods for addressing how to avoid lower back injuries have also become quite standardized. However, we are still trying to answer Dubos’ original question today. There are typically two ergonomic approaches to answering the question: (1) engineering or (2) administrative controls.
The engineering solution looks at how to improve the physical environment, such as the redesigning of tools and the layout of the job. However, the ergonomist is rarely able to quantitatively state that what they did had an actual positive impact on the movement and behavior of the worker. One way to address the problem quantitatively is by conducting biomechanical studies pre- and post-intervention including changes to the work environment. One such study, conducted by Jorgensen et al.3, demonstrated that there is no difference in movement behavior of the torso kinematics during a palletizing task when the pallet is close to versus far from the point of origin of the lift. These types of studies can help companies make informed decisions prior to implementing potentially costly work and material flow changes on a wide scale.
Administrative solutions look at factors such as job rotations, work-rest schedules, and training. Risk injury can be determined by calculating the time weighted average4, which multiplies the risk scores by duration of time a worker performs a specific job and then sums all these products. Frazer et al.5 examined the effect of job rotation and found that there is a linear transition of the time weighted average when going from a low-impact job (i.e., one that places little stress on the spinal cord) to a high-impact job (i.e., one that places larger amounts of stress on the spinal cord). However, it was discovered that the opposite is not true as the transition of the time weighted average from a high-impact job to a low-impact job is not linear. Therefore, it is difficult to determine the true effect that job rotation has on reducing back injuries, and more studies in this area within a poultry plant are needed to establish any definitive guidelines.
Van Dieen6 evaluated different work schedules for tasks requiring standing and demonstrated that when optimizing for the visco-elastic nature of the spine, multiple short breaks are recommended; however, when optimizing for lower extremity swelling, longer breaks are necessary. Van Dieen recommended observing a 3:1 work-rest ratio. Merely telling someone how to lift an object is not sufficient when trying to reduce their risk of back injuries if they do not have the muscular strength to do the task appropriately. Incorporating strengthening and endurance exercises into training may reduce the overall risk of back injuries. However, what still remains unclear is the feasibility of these conditioning solutions given the work demand and environment. Very few scientific studies have been conducted in poultry plants to aid in these assessments.
Have the engineering and administrative controls been effective in reducing lower back injuries in poultry processing operations?
According to Hammock7, the highest recorded incidence of lower back injuries in poultry processing operations between 1992 and 2007 occurred in 1994, with 170 cases of nonfatal occupational injuries and illnesses being reported that involved days away from work. Over the past 25 years, there has been a decline in lower back injuries; however, in the past 10 years, there has been no significant change with the industry averaging approximately 35 cases per year over the past 10 years (see figure below). This suggests that the engineering and administrative controls have been successful, up to a point. So, what else can be done? McGill8 suggests in his position paper that perhaps it has come time to “fit the person to the task,” in the sense that workers can retrain the way in which they move so as to minimize their risk of injury. What remains to be considered is the human factor. Common wisdom suggests that perhaps stretching the muscles prior to the task may reduce the risk. However, this has no scientific merit, and it has been demonstrated that stretching has no affect on the risk of injury9. The Biering-Sorenson10 study showed that greater range of motion of the spine and less extensor muscle endurance resulted in an increased risk of first-time back injuries. In order to determine how to best “fit the person to the task,” one needs to understand the difference between how the worker actually does the task versus how the ergonomists perceive that the task is being completed. The only way to do this quantitatively is by comparing biomechanical analysis pre- and post-interventions.
Managing profit by investing in ergonomic interventions is a complicated matter and will vary between companies and between plants. Therefore, it is important that such a cost analysis be done at both the plant and company level. Hughes and Nelson11 recently developed a mathematical model to estimate the net present value of cash flow as a direct result of the investment in the prevention of lower back pain. They use a combination of biomechanics, epidemiology, and finance in an integrated tool to aid in the assessment. Before one moves forward with further interventions, it is prudent to assess the financial implications.
In conclusion, the ergonomics of lifting have come a long way since 1977, and we have seen direct results of implementing both engineering and administrative standards through the reduction in lower back injuries within the poultry industry over the past 25 years. However, there is still work that remains to be done to further reduce the incidences of lower back injuries from the workplace, such as understanding how slippery floors contribute to lower back injuries and miniaturizing biomechanical devices to quantitatively measure workers movement behavior in real-time. A truly collaborative effort between industry and the ergonomics community will be required if we hope to see a continued decline in lower back injuries, but the good news is it can be accomplished.
Linda Harley is an Applied Physiology graduate research assistant in the Georgia Tech Research Institute’s Food Processing Technology Division. She can be contacted by email at linda.harley@gtri.gatech.edu.