Physics of Lifting and Spine Load

Study Notes

Larger forces are required to lift an object quickly, which are transferred to the spine, increasing the risk of injury.
Asymmetric postures increase the muscle forces needed to counteract gravity, leading to higher compression and shear on the vertebral motion segments.

Grasping or holding the load at a distance from the trunk increases the risk of injury.
Twisting the trunk while supporting or lifting a load increases the risk of injury.
Lifting or lowering objects placed below knee or above shoulder height increases the risk of injury.
Lifting or moving the load through large vertical or horizontal distances increases the risk of injury.
Holding or carrying the load for long periods increases the risk of injury.
Lifting or carrying frequently increases the risk of injury.
Lifting while seated increases the risk of injury.

Confined spaces decrease the ability to exert forces, increasing the load on the trunk muscles.
Height of object: only items placed between knee and elbow height should be lifted.
Flooring: space for the feet should be provided, and slippery floors should be avoided.

The abdominal and thoracic muscles play a major role in stabilizing the spine when lifting a weight.
Spinal compression is increased when loads are lifted, and even more when lifted quickly and with asymmetric posture.
Lifting technique influences manual handling efficiency, and it is recommended that the hip extensors should play the major role in powering the lift.

The trunk can fail in three ways when lifting: muscle and ligament failure, intervertebral disc herniation, and abdominal contents extrusion.
Back injuries are often referred to as ‘muscle strains or tears’, ‘prolapse’ discs, and ‘hernias’.
Disc prolapse is not simply caused by a sudden event, but rather the end product of years of degeneration of the disc and surrounding structures.

Use mechanical means (e.g. hand trucks, pushcarts, etc.) when possible for heavier or awkward loads.
It is easier and safer to push than to pull.
Keep loads as close to the body as possible and do not twist while lifting, carrying, or setting down a load.

Exoskeletons: devices that can be used to supplement the human body when completing tasks that require repetitive motions or strength.
Overhead cranes: can drastically decrease the exposure to workers for lifting and moving heavy objects.
Handles and grip aids: can change the posture of the lift and reduce pressure points while lifting.
Forklifts: powered vehicles that can pick up significantly heavier objects compared to the human and move it to a new location.
Pallet jacks: can assist in moving heavy objects, and can be both powered and manual.

Assign the job to more than one person.
Use smaller containers.
Mechanize the process.
Machines, rather than employees, should transfer loads between surfaces.
Change the job from lifting to lowering, from lowering to carrying, from carrying to pulling, and from pulling to pushing.
Use handles, hooks, or similar tools to enable workers to get a firm grip on objects to be lifted.
Reduce the weight of containers used to transfer objects.
Balance and stabilize the contents of containers to avoid sudden shifts in load during a lift.
Design containers so that they can be held close to the body.

Increase the height at which the lift is initiated; decrease the height at which it terminates.
Stack objects no higher than shoulder height.
Store heavy components on shelves between shoulder and knuckle height.
Avoid deep shelves.
Avoid side to side lifting from a seated position.
Provide access space around components to cut down on the need for manual repositioning.
Storage bins or containers should be fitted with spring-loaded bottoms.
Use sloped surfaces to gravity-feed items to the point of lifting.
Provide free space around and under the work surface to increase functional reach.