Why does my arthritis hurt more in the morning and get better throughout the day?

Inflammatory disease: Inflammatory arthritis is usually worse in the morning or after periods of rest when byproducts of inflammation build up in the joints. Moving and being active increases the rate of clearance of these inflammatory products from the joint. In contrast, degenerative, or wear and tear, arthritis typically is worse with use and better with rest.

Expected: Several forms of arthritis have this feature. As to the exact mechanism, nobody knows for certain.