the idea of movement.... just transferred from the Nude (Nude Descending a Staircase, No. 2 - Duchamp painted this in 1912) into a bicycle wheel (Bicycle wheel, his early ready-made from 1916-17).

Duchamp is looking back shortly before his death in 1968; as quoted in Looking at Dada, eds. Sarah Ganz Blythe & Edward D. Powers - The Museum of Modern Art New York, ISBN: 087070-705-1; p. 41