Build-up of lactose in athlete's initial runs (10)
I believe the answer is:
escalation
'build-up' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'lactose in athlete's initial runs' is the wordplay.
'initial' suggests taking the first letters.
'runs' is an anagram indicator.
The initial letter of 'athletes' is 'a'.
'lactose'+'in'+'a'='lactoseina'
'lactoseina' is an anagram of 'ESCALATION'.
'of' is the link.
Can you help me to learn more?
(Other definitions for escalation that I've seen before include "sudden rise" , "expansion" , "Rapid rise in level" , "Rapid growth" .)