Regular exercise — shaving seconds off an Olympic record? (8)
I believe the answer is:
periodic
'regular' is the definition.
(thesaurus)
'an olympic record?' is the wordplay.
'an' becomes 'per' (synonymous as in 'once an hour', 'once per hour').
'olympic record?' becomes 'iodic' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'per'+'iodic'='PERIODIC'
'exercise shaving seconds off' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
(Other definitions for periodic that I've seen before include "Recurring at regular intervals" , "Intermittent" , "Cyclical" , "every now and then" , "Occasional" .)