Grapnel is broken, and deteriorating (9)

I believe the answer is:

relapsing

I'm a little stuck... Click here to teach me more about this clue!

'deteriorating' is the definition.
The answer and definition can be both related to bodily activities as well as being present participle verbs.
Maybe you can see a link between them that I can't see?

'grapnel is broken' is the wordplay.
'broken' indicates anagramming the letters.
'grapnel'+'is'='grapnelis'
'grapnelis' anagrammed gives 'RELAPSING'.

'and' is the link.

Can you help me to learn more?

(Another definition for relapsing that I've seen is " sinking".)

I've seen this clue in The Daily Express.

Want a hint initially instead of a full solution? Install my app