I was a 2-3 metre worst thrower working full time then being a student. I was not an elite athlete by any means but I trained 3-4 hours a day plus did as much recovery work as I could. The first 6 months of full time work and part time study on top of training my distances dropped by 7 metres, I became a bit smarter with programming for me and improved.
Oh sitting at a desk is not physically tiring, but mentally I was spent most weeks. Which I have found to be harder then physically tired.