I get into training for mine (3)
I believe the answer is:
pit
'mine' is the definition.
(as in a mining pit)
'i get into training' is the wordplay.
'get into' indicates putting letters inside.
'training' becomes 'pt' (Physical Training).
'i' inserted within 'pt' is 'PIT'.
'for' is the link.
(Other definitions for pit that I've seen before include "Match (one's wits); mine" , "Mine-shaft" , "Deep hole (in theatre?)" , "Tip into miners' shaft" , "Large hole; mine" .)