A race covering one mile demands energy (9)
I believe the answer is:
animation
'energy' is the definition.
(animated can mean energetic)
'a race covering one mile' is the wordplay.
'race' becomes 'nation' (both can mean a national or ethnic group).
'covering' indicates putting letters inside.
'one' becomes 'I' (Roman numeral).
'mile' becomes 'm' (common abbreviation).
'i'+'m'='im'
'nation' enclosing 'im' is 'nimation'.
'a'+'nimation'='ANIMATION'
'demands' acts as a link.
(Other definitions for animation that I've seen before include "Liveliness - illusion of movement in cartoon films" , "Making of cartoons" , "Cartoon technique" , "Liveliness and enthusiasm" , "Film technique; lively state" .)