تعريف ومعنى "[keep] in (good|) trim"

What is the origin of the idiom "keep in trim" and when to use it?

The idiom "keep in trim" originated in the early 20th century and is believed to have been derived from the nautical term "trim," which refers to maintaining a balanced position of a ship in the water. It has since been used metaphorically to describe the act of keeping oneself or something in good condition, often in terms of physical fitness or maintenance.