Physics of Lifting and Spine Load

Manual Handling and Postural Stress

• 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.

Task Factors that Exacerbate Postural Stress

• 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.

Workspace Factors that Exacerbate Postural Stress

• 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.

Anatomy and Biomechanics of Manual Handling

• 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.

Back Injuries and Lifting and Carrying

• 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.

Important Things to Remember during Manual Handling Tasks

• 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.

Equipment to Reduce Risk of Injury

• 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.

Steps to Minimize the Weight to be Handled

• 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.

Steps to Minimize Reach and Lift Distances

• 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.

Steps to Increase the Time Available for Lifting

• (No specific information provided)