Clean and lube the drivetrain regularly. It may not get exposed to the dirt and grime outside, but the motion still creates wear. Frequency will depend on your total usage, but if you follow a similar timing to outside usage, you should be good.
Also, depending on your fans and cooling, if you are dripping even moderate amounts of sweat on the bike, you can ruin major parts. Things like head sets, wheels, and handle bars can all be permanently damaged from excessive sweat if left in place.
So, make sure you have LOTS of cooling via fans and cool air from outside if possible. If you still sweat on the bike, clean it and remove the sweat after EVERY workout. You may also want to remove and replace the bar tape each season, because it can hid dangerous corrosion that can lead to a broken bar.
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