Never twist your body when holding something. It is common for me to ask a patient with low back pain how he hurt his back and he responds that he was holding a heavy box and twisted his back. This is one common way to cause a disc in the low back (lumbar spine) to bulge or herniate, which is a very common diagnosis in PT clinics. The complication associated with disc problems is that if a lumbar disc bulges out of its normal position, it can compress the nerves in the spine, causing pain and other symptoms into the leg or legs. It is much easier to prevent a disc herniation than to treat one after it occurs!
Here is a video showing what not to do. I posted it a year ago, but it’s funny and worth another viewing.