Taking the Guesswork out of Lifting
Many comedians have pretended to lift a box that looks heavy to get a laugh. The box turns out to be light, and the jokester falls over. This may be funny on the stage, but it's a serious problem for workers. People who lift and handle items for a living are called manual material handlers (MMHs). Back injury is their number one enemy.

Lifting a load of unexpected or unknown weight is dangerous. The lifter may think it weighs more than it does. Getting the body ready to lift an object depends on knowing how much the item weighs. Using more force than is needed to move materials can increase the risk of falling backwards. The same risk applies to unstable loads or loads that shift suddenly, such as liquids.

MMHs must prepare their bodies each time they lift an object. The muscles and body posture are part of this preparation phase of lifting. Keeping the center of gravity steady is an important part of keeping balance without falling over.

Bending the trunk closer to the object lowers the center of gravity. This is called the stoop method of lifting. Stooping or bending over to lift puts greater strain on the low back. It's easier to keep balance with the stoop method compared to the squat method of lifting.

Scientists are studying ways to prevent injuries for MMHs. More research is needed to mimic actual work settings. This will provide helpful information for different jobs where varying loads are lifted.
References
Yung-Hui Lee, PhD, and Tzu-Hsien Lee, MS. Human Muscular and Postural Responses in Unstable Load Lifting. In Spine. September 1, 2002. Vol. 27. No. 17. Pp. 1881-1886.