What’s the science behind feeling shutdown after a few days off the bike?

Had a really good training session going for a while there. Hitting new VO2 numbers on intervals each week. Really pleased with progress.

On a recovery week after 3 weeks of hard work and ended up with 3 whole days off the bike unintentionally. Day 4 today and jumped on trainer to wake legs up and although legs when walking around felt good, they felt dead on the bike. So dead that I quit a few mins into an endurance interval!

Ended up doing some 30sec intervals at threshold to wake them up but all those felt like a slog and my HR was low.

I’ve seen other guys talk about this but this is probably the most eye opening I’ve experienced myself. That Indan remember anyway. Was kinda expecting to be super fresh!

I’ll try again tomorrow but for now I’m wondering what exactly is the science behind this and how can it be avoided while still recovering really well.

I like taking full days back to back off the bike now. Finding I’m making more progress than I used to. Usually do a lot of 2 days, but 3 broke it?