> 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.
~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.