Do too much exercise in obvious downpour (9)
I believe the answer is:
overtrain
'do too much exercise' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'obvious downpour' is the wordplay.
'obvious' becomes 'overt' (similar in meaning).
'downpour' becomes 'rain' (pouring rain).
'overt'+'rain'='OVERTRAIN'
'in' is the link.
Can you help me to learn more?
(Other definitions for overtrain that I've seen before include "Run past peak, perhaps" , "Prepare too hard" , "Spend too much time on exercises" .)