Form has changed with training (5)
I believe the answer is:
shape
'form' is the definition.
(I know that form can be written as shape)
'has changed with training' is the wordplay.
'changed' indicates an anagram.
'with' means one lot of letters go next to another.
'training' becomes 'PE' (Physical Education).
'has' anagrammed gives 'sha'.
'sha'+'pe'='SHAPE'
(Other definitions for shape that I've seen before include "Good physical form" , "Phase (anag.)" , "Control development of" , "Form, figure" , "External form" .)