Why is it important to be careful about lifting?

From Healthwise

Back injury is best avoided at all costs. Once you have injured your back, it becomes more vulnerable to future injury. A back injury can alter your entire quality of life and possibly your livelihood, especially if it returns or becomes chronic.

Poor lifting technique can injure your back in various ways:

• Muscle or ligament strain—or tiny tears in the muscle or ligament—commonly results from a combination of poor body mechanics and too much of a burden on your back muscles.
• Spinal disc injury is often caused by forward bending of the spine and poor lifting technique. A spinal disc that is squeezed by the vertebrae above and below it can bulge or break open (herniated disc), causing back and leg pain and numbness (sciatica) and occasionally bowel and bladder problems.
• Vertebrae can become damaged during awkward lifting.