Can someone explain the physiology of the "Second wind"?

Maybe you slowed down for a bit and recovered.

Beans.

You started too fast, recovered, then got back up to your desired race pace.

A very old reference on it is George Sheehan, in Dr. Sheehan on Running (1975, maybe or maybe not still in print). As I recall the first "second wind" you experience is essentially when you are warmed up, after just a mile or so. Your breathing gets into a rhythm then and the effort is easier. The research from those days also found a later second wind as you described. I don't recall how much he went into the physiology of it as that's the least interesting thing in the world to me (I wanna know what happens, don't care why).

Yep, it's called "You're warmed up"

An early second wind is just being fully warmed up. A later second wind has to do with energy sources and how you are using them. It's not pace related.

I bet a bit of it is psychological. You get 3/4 into your run and you’re stimulated by feeling better than you expected and knowing you’ve only got a little more to go. I always go out with consternation and stress, but I relax as I start to make my way through the run.

Central governor theory:

https://en.wikipedia.org/wiki/Central_governor

Fatigue is highly psychological. The second wind is mostly about breaking through a psychological barrier, whereby your brain allows your body to take on more physiological stress than normal.

The problem with that thinking is that the second wind often just happens when you're not thinking much at all.

Also it has little bearing on where you are in a run so it proximity to the end doesn't have much to do with it. Many times people add onto a run that suddenly starts going well.

Ultrarunners sometimes go from near collapse to miraculous turnarounds at random points. Didn't Jenn Shelton collapse and then get up and run around a 3 hour marathon in the middle of an ultra?

Just saw this doc called “The Source” about Courtney Dauwalter doing a 200-miler. She has some major nausea about 12 hours in then does the last 140 miles without eating. These ultra runners are crazy https://m.youtube.com/watch?v=DQSiygnDm-U

You obviously get progressively more tired while you run, but you also lose weight while you are running. At some point, your weight loss begins to predominate over the fatigue effect, and you start running faster just because it is easier to run with less weight to carry.

Agree with the person who said it is more psychological. For example in mile races, the third lap is often the slowest, but the finial lap is often the fastest.

I think ultrarunners have psychological issues...not necessarily a bad thing but it's far from normal. There is just something "off" about them. Maybe they're running as a way to forget about some other issue. If you're just running 10 hours for the sake of running, there's no way you're doing it for the pure enjoyment of running. You're working through something. Whether it be self-doubt or something else.

bartholomew_maxwell wrote:

I think ultrarunners have psychological issues...not necessarily a bad thing but it's far from normal. There is just something "off" about them. Maybe they're running as a way to forget about some other issue. If you're just running 10 hours for the sake of running, there's no way you're doing it for the pure enjoyment of running. You're working through something. Whether it be self-doubt or something else.

Ultra runners are the extreme version of the fat ladies who run just so they can put it on social media. Some of them go to extremes to do something really weird they can share it but many of them just cheat and say they did.

mind over physicality wrote:

Agree with the person who said it is more psychological. For example in mile races, the third lap is often the slowest, but the finial lap is often the fastest.

The second win would be in the third lap if it mirrored a typical training second wind.