A disc in my lumbar is more messed up than a soup sandwich, so it limits heavy material handling.
So, using the old adage "Think smarter not work harder" I reevaluated how I was handling the moving of dirt, rock, etc.
I had already bought a nice Ace Hardware contractor wheelbarrow with two front wheels. While this is not quite as easy to maneuver across uneven ground or in tight spaces, it kept me from tilting my back side to side trying to balance the load. I took its tire track width into consideration when designing the garden walkway paths.
And I've used a small nursery cart as well, along with a dump cart. About $80 each and well worth it. The dump cart is totally worn out after a decade of hard use.
But, the biggest problem was handling transport and moving gravel and drain rock. This was bought in bulk and put in my pickup bed. I had to break my back shoveling it out of the truck, then moving a load with the wheelbarrow.
So, I bought enough Homer buckets from Home Despot to fill up the truck bed. I found my max lifting load to be between 2/3rds of a bucket with gravel and 3/4 of a bucket with wet earth. At the gravel yard I either hand fill a few buckets for small jobs, or lay them all out and have the scoop operator fill them. I then dump out the excess to get the weight down, and put them in the truck. At home, lift them out and stack two on a handtruck with large tires. This has worked out very well for me. On top of that, I can put store a few of these buckets of gravel and not have a pile of gravel making a mess.
Drawback with Homer buckets is they only last maybe two to three years at best. The plastic becomes brittle. I don't mind when the bottom gets a crack in it, as this helps the bucket drain. But the tops start cracking and breaking. Still, they are relatively cheap and readily available.