I think speed is a good indication. I've thrown a bit of a monkey wrench into it by building a "new" bike. And, am still working on bike improvements.

But, I have an 11 mile out and back course that I've been pushing on. My personal goal is to do it twice at 20 MPH. But, so far I've hit it once at 20 (up 1 MPH from my last run). And, I'm routinely holding it above 20 MPH for longer on other rides and segments. I've hit several PRs in the last month on segments with previously doing hard efforts.

As far as "winded". Doing a 35 to 40 mile RT from Mom's house to mine and back used to be a bit of an ordeal, and it is pretty routine now. And the recovery time for my short/steep driveway segment is much quicker.

Another element is that knee pain has been reduced significantly since increasing my mileage.

And, my weight is stable, well, actually in a gentle downward trend.

I suppose I should have done thigh measurements.