Use double the kinetic energy on stationary machine with pedals (8,4)
I believe the answer is:
exercise bike
'with pedals' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'use double the kinetic energy on stationary machine' is the wordplay.
I cannot quite see how this works, but
'use' could be 'exercise' (synonyms) and 'exercise' is present in the answer.
'energy' could be 'ke' (K.E. is an example) and 'ke' is present in the answer.
The remaining letters 'bi' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for exercise bike that I've seen before include "Stationary keep-fit equipment" , "Vehicle going nowhere?" , "Gymnasium equipment that will get you nowhere!" .)