Go out of shape, permanently (3)
I believe the answer is:
pep
'go' is the definition.
(both can mean energy or vitality)
'of shape permanently' is the wordplay.
'of' indicates a hidden word.
'PEP' is hidden within 'shape permanently'.
'out' is the link.
(Other definitions for pep that I've seen before include "Palindrome for vitality or energy" , "Go" , "savings plan" , "Ginger; tax-free investment" , "Energy or enthusiasm" .)