Number one in lifting 80% excess weight (4)
I believe the answer is:
self
'number one' is the definition.
(I've seen this in another clue)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for self that I've seen before include "Will the author" , "A person's awareness of their own identity" , "Will the writer?" , "Will perhaps" , "one's identity" .)