in the groove

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

Prepositional phrase

 * 1)  Running or performing extremely smoothly, especially  playing perfectly, perfectly in sync with others, or with perfect focus.
 * 2) * 1933 Aug., Fortune, p. 90:
 * The jazz musicians gave no grandstand performances; they simply got a great burn from playing in the groove.
 * 1) * 1869, J.E.T. Rogers's preface to 's , Vol. I, p. 27:
 * The whole course of legislation... had flowed in the same groove for centuries.
 * 1) * 1932 Oct., Melody Maker, p. 836:
 * having such a wonderful time which puts me in a groove
 * having such a wonderful time which puts me in a groove

Synonyms

 * in the pocket, in the zone