Why is it that when you lift object at certain height and hold there for some is not considered work?

Work is defined as the effort (force) to move an object (mass) a given distance. While holding an object at a height is strenuous for humans, this is not because we are doing work, but because we are resisting gravity. This makes sense if you consider inanimate (non-living) objects: for example, does your chair struggle when you sit on it?