The three main subjects long distance runners think about:
 
1. pace and distance
 
2. pain and discomfort
 
3. the running environment, especially those nasty hills, and the weather
 
If you were wondering if long-distance runners use this time to solve life’s dilemmas – relationship troubles or metaphysical conundrums, for example – it seems that is not the case.

Samson, A., Simpson, D., Kamphoff, C., & Langlier, A. (2015). Think aloud: An examination of distance runners’ thought processes International Journal of Sport and Exercise Psychology 1-14