My mother was an OTR trucker during most of my teenage years, including driving for Walmart under contract (so not paid amazingly well, but regularly interacted with the Walmart employees at the DC in Tomah, WI). It's not always back breaking work, but access to (healthy) food is a major issue. For Walmart specifically, there's not much physical effort involved besides lowering the trailer landing gear, which is almost always done with a manual crank. The Walmart backroom staff handle unloading and the DC staff handle loading, which would be very very taxing to do constantly.

why is access to healthy food an issue? because truckers, being on the road, have to eat in poor quality restaurants, such as diners, maybe?

In a truck you can't just... drive anywhere. There are designated legal routes that you can't deviate from under most circumstances. The vast majority of food you have access to as a trucker is gas station/truck stop food and fast food attached to truck stops. You have limited cooking options in a truck, maybe a small waffle iron, rice cooker, or microwave. Most won't have room or power for something like a refrigerator (some might, it depends) so keeping non-dry food isn't really an option.

First, your work day is almost completely sedentary. Second, you are not near friends, gyms, fields, or other systems which promote healthy activity outside of work. While diet is important for all of us, it is especially important in this circumstance.

"Healthy foods" are going to be largely inaccessible through long sparsely-populated stretches of the country. Even where they are available - in markets, fruit stands, etc. pulling your huge truck off the road to park is expensive (in terms of time) and difficult (in terms of space). Truck stops have the infrastructure for your truck. But their food selection is mostly junk.

They generally don't have access to a kitchen or a large refrigerator, so meals tend to either be from a restaurant (where most restaurants, good and bad, are arguably not healthy unless you severely portion-limit) or something that can be reheated in a microwave or portable air fryer. In combination, this results in a not quite healthy diet.

thanks to all for the good answers.

What is it in particular about truck driving that is so bad for your back? I hear this so often.

Please don't reply "sitting down all day". I have been doing that for more than 20 years in a comfortable office (mostly Hermann Miller Aeron), and my back is fine.

My guess: The vibrations of the truck are awful for your bones.

Do you ever get up? Maybe turn your head from side to side, or stretch your legs out under your desk? Or go to the bathroom whenever you want?

Driving freezes your body into one position for hours on end. Doing it in a car for a few hours on a road trip makes my neck hurt. Doing it every day would be deleterious very quickly.

I work at a computer at a desk, but the ability to stand up at will just to use the toilet makes a big difference. Can’t do that driving a truck.