Did some crossfit for awhile. Very high intensity. Despite having some unusually experienced coaches with degrees in Kinesiology and PE, people still were injured. They did great warmups and lessons on proper form (much better than college classes I had) but I believe it was that every workout was timed. As you get to the end of what you are capable, you lose form. Everyone is shouting at you to keep going. Being in a hurry makes it easier to cheat on proper form.

I have had some long days were I carried a big pack for 14 hours of more of cross country, but the distances wouldn't be as impressive as if un-burdened.

Years ago hiked 22 miles up to the top of the North Cascades and back with 5000 ft of elevation gain and then loss, on a search. Then ran a 9 mile foot race in the afternoon. It is where I met my wife. She did it too.

When in college rode a bike most of the way across France one day from La Rochelle to Lyon with temps over 100 F. Must have drank 2 or 3 gallons of sweetened water with salt trying to recover that evening. It was the longest day of a 3 month bike tour of Europe. We averaged 70 miles a day. After the initial few of weeks getting used to biking, 70 miles (mostly flat) seemed very doable at about 12 miles an hour. Once we tried hiking after a day of riding and our legs wouldn't work right, so much so it was comical to watch each other.