Wiktionary
n. (rfquote-sense: en) exercises designed to promote physical fitness if performed regularly. vb. To exercise for physical fitness.
Wikipedia
Keep Fit is a 1937 British comedy film directed by Anthony Kimmins and starring George Formby, Kay Walsh and Guy Middleton. It was made at Ealing Studios. Formby was at his British top box-office peak when this comedy was made.
Usage examples of "keep fit".
And that'll mean as long as they keep fit and can keep playing football then they won't die.
I had been riding as an amateur in jump races since my sixteenth birthday, but was now, with thirty-two in sight, finding it increasingly difficult to keep fit.
The human body was meant for motion, and this small group of women was still doing what they could to keep fit.
Paul had worked for fifteen years in the same dreary office in Luton and, from what I had gathered during the course of investigating his life he hadn't done much to keep fit.