never stand still, n. — Green’s Dictionary of Slang

never stand still n.

also can’t-keep-still

[rhy. sl., accentuated by the endless movement of the machine]

a prison treadmill.

1892		‘Doss Chiderdoss’ ‘The Rhyme of the Rusher’ in Sporting Times 29 Oct. n.p.: The once a week made me go ta-ta / For a month on the can’t keep still.
1960		J. Franklyn Dict. of Rhy. Sl. 46/2: can’t keep still Treadmill. 19 C.
1984		Partridge DSUE (8th edn) 179/2: ca. 1850–90.