Materials handling is a challenging job physically. In addition to garbage cans, collectors also lift and swing plastic bags, boxes, and containers of all sizes.
The most common problems for the worker are judging the weight of the object being lifted and loads that shift inside the container while being lifted. You can’t change the size, weight, or shape of public trash.
You can, however, encourage workers to test the object before picking it up. This is especially important when lifting two refuse bags, one in each hand. Any size or weight different can increase the risk of back injury.