One may be found in bed, knocking back excellent fruitcake after workout (7)
I believe the answer is:
petunia
'one may be found in bed knocking' is the definition.
I can't tell whether this defines the answer.
'back excellent fruitcake after workout' is the wordplay.
'back' says the letters should be written backwards.
'excellent' becomes 'ai' (resembles 'Ae', old-fashioned term for excellent).
'fruitcake' becomes 'nut' (I've seen this in another clue).
'after workout' becomes 'ep' (I can't explain this - if you can you should believe this answer much more).
'ai'+'nut'+'ep'='ainutep'
'ainutep' backwards is 'PETUNIA'.
Can you help me to learn more?
(Other definitions for petunia that I've seen before include "Popular plant for baskets" , "Bloomer" , "Garden plant with large funnel-shaped flower" , "Flowering plant" , "Flower - tuna pie (anag)" .)