When you are lifting something heavy, bend your knees, not your waist. Use your legs to support the weight. You'll put less pressure on your back that way.
That is such an important tip! I am dealing with arthritis in my spine as well as herniated discs because of years of misuse and abuse on my back. I think as gardeners one needs to be especially careful because it is not always apparent how much strain one is putting on their backs.
