A person carrying a heavy bag normally finds the impact of the weight differently if he carries it in different ways. For example if he carries it by the handle or by a strap on the shoulder or putting the whole bag on top of his shoulder. Why is this so (as the weight of the bag is the same in all the cases)?
the leverage on the body of weight hanging at differing points has a different torque on a bone, and the muscles have to supply differing forces to hold it.
When digging, where you hold the shovel makes a big difference on the force you have to apply.