Pete Kostelnick just ran across the US in 42 days breaking the prior record by 3 days. I guarantee you he tolerated a lot of suffering:

http://www.nytimes.com/2016/10/26/well/move/how-to-run-acros...

Then there are events like the Badwater 135 and the Vol State which seem surgically designed to inflict suffering:

https://ultrasignup.com/register.aspx?did=34762

Or the Marathon de Sables:

http://marathondessables.co.uk/

Or how about the 52 day Sri Chinmoy Self-Transcendence 3100 Mile Race in Queens, New York City:

http://3100.srichinmoyraces.org/

I recently participated in my first 24h foot race, completing 105 miles. Nearly 400 of us running a 1.5 mi loop around a lake for hours on end. Why do we do these things? I had a whole day on my feet to contemplate that question and I never came up with a satisfactory answer. I finally decided there is no why. We do it because it's there. And maybe because we have a bit too much time on our hands. Nonetheless, I find this text from the Vol State link poetic:

Many will fail. But, for those who find the steely will and muster the sheer dogged tenacity to overcome the impossible obstacles, and reach the rock on foot, the Vol-State can be a transcendental experience. No words can adequately describe the sense of combined relief and amazement to be experienced at the Rock. No one can explain the regret that this incredible journey has actually come to an end. Former King, Barry Crumrine probably summed up the Vol-State experience as well as it can be put into words: “I found in myself something that I never knew was there.”

Suffer well my friends.