"Warming a chair" means to be sitting in a seat for a prolonged period without doing any work. The antonyms of this phrase are "productive", "active", "working", "engaged", and "contributing". These words imply that a person is using his time wisely and is focused on completing a task, rather than just occupying a space. The opposite of "warming a chair" can also be described using phrases like "moving", "in motion", "getting things done", "being proactive" and "being useful". These antonyms highlight the importance of constant action, work, and productivity in our lives rather than merely being idle.