There a few factors to take in to consideration when lifting, and those factors should be in the forefront of your mind when faced with a light, moderate, or heavy load. The first thing to remember about the body is the legs are one’s “powerhouse”, so the primary muscles working when lifting should be your legs! Bending the knees at a wider stance and engaging those major muscles in your legs, such as your hamstrings, quadriceps, and gluteal muscles are crucial when lifting.
Another factor to consider when lifting is how close the object is to/from your body throughout the lift. To minimize the forces and strain on your spine, which is a pretty delicate part of the body, you really must keep the object as close to the trunk as possible. The farther the weight is from the body, the larger the weight will appear to be according to your spine! For example, a 10 lb. box will appear to weigh 10 lbs. if held firmly against the body when holding and lifting. However, if you are to extend your arms with that same 10 lb. box, the weight multiplies by 10, so now the spine thinks that the box weighs 100 lbs.!
One other crucial factor to consider when lifting is to avoid twisting the spine while carrying a heavy load. As already mentioned above, the legs are the “powerhouse” of the body and it is best to move the feet in order to turn, or transfer a load from point A to point B. It is inevitable that the many muscles of the trunk will engage when lifting anything of weight (as opposed to solely the legs). When this happens it would be safer for all of us to avoid twisting the trunk because a combination of motions and demands on the muscles can cause faster muscle fatigue, and therefore injury (if the task is not completed!).
The most important thing to think about when preparing to lift is knowing the amount of weight in the load and understanding what your body can handle! Remember to bend the knees, to keep the object close and to avoid twisting whenever possible.