Using a backpack to transport heavy items that are too cumbersome to carry can actually be a bad a thing if it’s done all the time. Although we have amazing tensile strength in our back muscles, we do tend to over do it with how much stuff we shove in our backpacks.
I recommend to my clients that they don’t carry more than 20 pounds at any given time. This considerably decreases the chance of straining your back muscles. I see high school students on their way home from time to time. This is a generation of kids that is going to have postural problems for years to come. These kids are carrying 60 plus pounds on their backs everyday. They walk all hunched over, during the years that are critical for the development of the body: teenagers are growing at such fast pace it’s hard to keep up. It’s also a time they form life long habits, for better or worse.
Purchase a rolling cart or rolling bag instead of schlepping stuff around in a backpack. If you have high school age kids, have them carry only what they need every day, 20 pounds or less, with shoulders back… many backpacks are like walking garages… filled with junk that never gets used or even looked at.