thanks? But, I don't know how that helps with the question I'm asking. I'm not complaining about an inability to recover, nor was I asking for nutrition advise. If anything, quite the opposite, but in ways that are different than when I was younger.

What I'm asking about a delay in the onset of fatigue after a long/hard workout (2-3 hour long run, or a 90-120min interval session, etc) of 24-48 hours, such that I "could" complete a second workout of some type in that 24-ish hr window.

for example, my current schedule looks something like this (I'm a pure runner these days):

Mon: 6 mi easy
Tue: 12 mi with 8 miles of 5% grade hill repeats @ 10km pace
Wed: 6 mi easy
Thu: 12-14 mi sometimes with about 6 miles of 1-2 mile repeats (3x2mi or 6x1mi or 2x3mi @ 10km pace)
Fri: 6 mi easy
Sat: 15-20 mile easy
Sun: various (could be off, could be 2-4 mi recovery, could be 10-12 mi easy)

Normally, Sunday would be 100% off...its filler for the 100/100s...right now.

What I'm experiencing is that Wed/Fri/Sun I often feel much better than I expect to based on the workout the previous day. So, I'm wondering if there is some way to "stack" things to make use of that "next day window". Perhaps?

Mon: 6 mi easy
Tue: 12 mi with 8 miles of 5% grade hill repeats @ 10km pace
Wed: 10 mi easy (maybe with 2x3mi @ HM pace?)
Thu: 6 mi easy
Fri: 12 mi sometimes with about 6 miles of 1-2 mile repeats (3x2mi or 6x1mi or 2x3mi @ 10km pace)
Sat: 15-20 mile easy
Sun: various (could be off, could be 2-4 mi recovery)

I'm sure that would need some tweaking, I mostly just rearranged the first week above. Wed might need to just be all easy, or something.

I mean I guess I can just try it, and see. I was just curious if others had experienced similar...and, had already tried to make some use of it?

FWIW: I find Garmin metrics to be absolute SHIT. I mean honestly, it gives me recovery times of 4 days, and never things I should even do a workout (constant suggestion to rest). Just trash for me, worthless.