Ergonomics and Correct Lifting Techniques
Why is it Important?
According to the Worker Health Chartbook, 2000 most of the nearly half million spinal injuries are in service, manufacturing and the retail industry. The most common sources of back injury involved lifting containers (26 %) followed by worker motion or position (17%) and parts and materials (12%). Sixty-three per cent of these injuries were precipitated by overexertion on the part of the worker.
The overwhelming implication from these figures is simply that most back injuries are probably the result of the accumulative trauma resulting from improper lifting. Unfortunately, there is an insufficient amount of emphasis placed on proper lifting technique in the work setting on the part of management probably in part due to the lack of understanding of the biomechanics involved.
What are Some Basic Biomechanical Principles Involved in Lifting?
We can observe the natural squatting posture of a child between 8 and 18 months to see that how inherently natural it is for children to first get themselves into a standing position to begin walking. They begin by taking a wide stance to balance the head and pelvis over the hips. As they begin to push upwards the pelvis drops to overcome a lack of development of the leg and spinal muscles. By functioning as hip extensors, the gluteal muscles take on most of the work.
What comes naturally to the child demonstrates the importance of how the pelvis and the spine coordinate with one another to bring about the continuous movement involved in lifting an object off the floor. The effective movement of the spine in the lifting of objects depends on the coordination of the hip extensor muscles with the erector muscles that run alongside the spine. The burden of the weight must be transferred from the hip extensors through the recruitment of the muscles and connective tissue on either side of the lumbar spine as they statically contract to effectively transfer the load into the shoulders and arms.
The spinal erector muscles that lie parallel to either side of the spine have a short lever arm and, are in fact, incapable of lifting loads over 20 kg (approx. 44 lbs). Their function is to support and protect the spinal joints. When these muscles are recruited incorrectly, forces are exerted on these joints so as to cause damage.
What are the Effects of Improper Lifting?
The complete lifting movement, when done correctly, prevents excessive compressive and shearing forces from concentrating in the lumbar spine. It is the excessive shear and flexion of the spine coupled with rotation that fatigues and tears the disc fibers and strains supporting ligaments. The result of chronic improper lifting then, concentrates forces at the facet joints and intervertebral disc. The result is a breakdown of this three joint complex and possible intervertebral disc disease and facet syndrome.
A healthy disc serves to transfer loads from one vertebra to the next. A degenerated disc may fail under excessive compression resulting in herniation or fracture of the vertebral endplates. Ligamentous injury or laxity may follow causing more instability in the vertebral three-joint-complex.
What is the Optimum Technique for Lifting?
The primary consideration when performing lifting tasks is protection of the spine and it’s supporting musculature. To do this we must modify our movements to the greatest biomechanical advantage. Due to the significant moment forces put on spinal structures during the lifting of heavy objects it makes more sense to break the load down into several smaller loads if possible. It is more preferable to increase the number of lifts with lighter weight than to attempt a single lift with a much heavier weight.
The idea is to center the load so as to avoid an asymmetrical posture while initiating the lift. Any lateral bending and twisting should be eliminated as much as possible. Loads coming off the floor should ideally be positioned between the feet so the center of gravity of the object is brought as close as possible to the spine. A wide stance enables the pelvis to be brought close to the floor and avoids the necessity of having to stoop at the spine to reach the load. This stance minimizes shearing forces at the spinal joints and puts the workload on the thighs and hip extensors. The load is then lifted to a standing position with the spine in a neutral, erect posture and the load held close to the pelvis.