"Fatigue" is about exhaustion so deep that the speaker stops feeling like a person and starts feeling like a piece of equipment. Each line describes a change: sweat becomes grease, hips become bone, feet become wheels. The word "turned" repeats, as if the transformation keeps happening, one body part after another, with no way to stop it.
The images pull in two directions. Grease and wheels belong to machinery, so the body seems to be running like an engine, worn down by constant motion. But "hip turned to bone" goes the other way. It suggests everything soft has been stripped away, leaving something dry and hard, almost skeletal. Together they show a body being used up.
The speaker sounds tired, but not dramatic about it. There's no complaint, just a flat, matter-of-fact list. That plain tone makes the mood heavy and numb. The speaker is too worn out to protest, and the short lines make the poem feel as drained as the person in it.