I've read that the best way to prevent a back injury while lifting is to increase the stability of the spine. What does that mean and how do I do it?
Another way to think about spinal stability is to look at how stiff are the spinal segments. A lack of stability or unstable spine is loose, possibly with slipping and sliding of the vertebral bones against one another. A lack of this type of stability results in greater shear forces.
A stable spine is one that is held in place by the ligaments and muscles without a lot of extra motion. Compressive forces are greater with a stiffer spine.
Stability can come from the core muscles or from the global back muscles. Core muscles are the deep, short extensor muscles that attach the vertebral bones to each other. Some of the abdominal muscles are also part of the "core."
Global muscles are the larger, longer extensor muscles of the back. Using the global muscles for repetitive lifting can result in fatigue and injury. That's why there's such a focus now on strengthening the core muscles.
Core training is offered on video and at health clubs around the country. You may even be able to find such materials at your public library. Pilates is a popular version of core training. A physical therapist or pilates instructor can help you get started.