Sometimes a standard run can feel incredible, and I now have a theory as to why.

Sept. 1, I had one of those runs at Tsalteshi Trails.

It was only 3.15 miles, taking place on loops I have done hundreds of times before — Wolverine, Goat and Coyote.

It was slow, averaging 12:06 per mile. In my defense, there was 259 feet of elevation gain and loss. But still, slow.

Yet, it was one of those runs where the shoulders and neck loosen with each stride. Where the air feels not only fresh, but like some magic medicine in the lungs. Where the sky is not blue, but azure. The clouds not white, but cottony.

But why? Puzzling over this question during the run, I vaguely remembered somebody talking about emotional velocity versus acceleration.

After a few Google searches that made me realize I have forgotten everything I learned in high school physics, I found this quote on “The Joe Rogan Experience” from Peter Attia, a longevity doctor.

“I would say that in life, velocity means very little. Acceleration means everything.”

When I took that run Sept. 1, my boss had just returned from a two-week vacation. Because there’s very little slack in the staffing numbers here in the newsroom, that vacation had me working 60- to 65-hour weeks.

While I was able to get out for runs, and even get to Tsalteshi a few times, those trips were always rushed. I had to get in to meet with the reporters, put together the opinion, wire and feature pages, and edit the news section. I had to complete all these tasks in time to engage in my late-night duty as sports editor.

Not only were the runs rushed, but most were in the rain or under very gloomy skies. As an Alaskan, I’m supposed to know there’s not bad weather, only bad gear.

But am I least allowed to say there’s such a thing as happy weather? The Grateful Dead wrote about words glowing with the gold of sunshine, and not with the sheen of falling rain, for a reason.

So Sept. 1, I accelerated from rushed jaunts with a touch of gray to a relaxed jog under brilliant skies with a golden leaf trickling from the sky or carpeting the trail here or there.

In the first half of the summer, I’d probably had 20 or 30 relaxed runs in great weather, but their day-after-day velocity was constant. That’s why Sept. 1 felt so good and so different.

The exuberance of positive acceleration is something I’ll try to keep in mind whenever I’m in a negative rut in any area of my life. All it takes is one simple act — read something in that stack of The Atlantic magazines, just clean something, anything in the bathroom — and the joys of positive acceleration kick in.

There’s more to learn from Attia’s concept than the ebullience of positive acceleration.

Earlier this summer, I was on an exercise roll when I damaged by toes by accidentally crunching my foot on a clothing chest in the dark.

The toes felt contused the next day. I didn’t care. I was at a velocity that I like in my workouts, so I went running anyway.

The next day, my toes and a good deal of the rest of my body felt wretched. I panicked as I took the next day off. Would I be out for weeks? Months? Had I broken something? It was only a day off, just like Sept. 1 was a standard run, but the negative acceleration made it brutal.

After another day off, I was able to run again without pain.

The positive acceleration meant everything.