What I have learned walking is that there is a period when you increase the effort either by adding weight to the pack or distance to the walk that I'm tired afterward, often for much if not all of the rest of the day.
In May I started walking 8 miles consistently at a 15-16 minute per mile pace. And I was tired for the rest of the day and had to take days off for errands around town, to catch up on stuff at home or work on the Website.
That has slowly changed in August as I found I'm not completely tired later in the day, which leads to two choice. I can either stay at this level and do more work, or I can up the effort to get better and fitter, and go through the cycle of being tired all over again.
And when does the latter stop? I've added another 0.5 to 1.0 mile some days and added another 5 lbs on other days and I'm back to being tired later but less and recover to work later in the day. This tells me the body is, albeit slowly, getting back to some sense of normal, but still some ways from normal.
So, that's where I'm at with the walking. Since hiking is usually 4-8 hours and roughly 6-12 miles roundtrip with significant elevation gain and loss, the walking still isn't sufficient to return to hiking more than 4-6 miles with a larger, heavier backpack.
The plan was to increase to 10 miles with 20 lbs, so I still have some ways to go, but the effort is reminding me that as you work, the effort is harder and longer, but the rewards are greater and better. And it's why maybe stopping at a level you're "comfortable" with maybe isn't enough.
Something to ponder on the walks, where do I stop to get better.