Athlete found up in Burren nursing home (6)
I believe the answer is:
runner
'athlete' is the definition.
(type of athlete)
'up in burren nursing home' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'in' indicates the answer is hidden within the clue.
'rennur' can be found hidden inside 'burren nursing home'.
'rennur' reversed gives 'RUNNER'.
'found' acts as a link.
(Other definitions for runner that I've seen before include "Canvas shoe with a rubber sole" , "done by con man, perhaps" , "Long narrow carpet" , "Groove or strip on which a drawer slides" , "Messenger; plant shoot" .)