Comment by IAmBroom

I used to run 5 miles a day on trails in a nature preserve. There were sections that were skewed to one direction, and dangerously so after rains. There were uncleared fallen trees to hop over. Etc.

One day, a coworker joined me. He was a serious runner, and was recuperating from a knee injury, hoping to compete again in a month or two. His pace, learned on tracks and city sidewalks, was so much faster than mine that I noticed him jogging in place when I hit a slow patch. After we finished, he went back and ran it again at his preferred pace.

Next Monday he reported that he had exacerbated his injuries on the trail, and would probably never be able to run again.

Talk about pushing yourself to the brink... I mean, if that course had been flat, he would have been fine. But his "high-level" techniques were honed on a course without the threats and extra challenges for his support muscles, and that combination ruined him.