in the groove

The story

Originally slang that first appeared in the mid-19th century with a (usually pejorative) reference to the difficulty of leaving a well-worn rut (see in a rut). As back in the groove, the phrase acquired a positive sense of returning to one's usual self after a period of illness, setbacks, etc. With special regard for music, originally US jazz slang from the 1920s, possibly with reference to the grooves of early records.