[jefftk]

> Barely, if any, difference between the sexes in races at this distance

This is 31 miles, which is not much longer than a standard 26.2 mile marathon. Marathons have a lot of competition, so we can see how top athletes compare, and there the record is 2:01 for men vs 2:15 for women. What you're saying is for much longer races.

[hprotagonist]

my understanding is that event distance and gender spread are not linear.

I believe there’s a wall at about 20 miles, too.

[ultrarunner]

> I believe there’s a wall at about 20 miles, too.

~20 miles is the distance that a "median" person can run before muscle glycogen is depleted and less efficient energy-production mechanisms must take up the slack. The size (and duration) of one's muscle glycogen stores depends on many factors, including the physical size of muscles, efficiency of reintroduction of liver glycogen, training status, running economy, GI effectiveness vs stress, and many others.

Interestingly enough, in longer ultras one gets the chance to conquer the "wall," recover, and then hit it all over again, maybe several times.

[jefftk]

It's hard to tell how much things like that reflect the shape of the maximum human performance curve, vs which sports are worth it for which athletes to reach peak performance.