But there were also other motivations that kept runners going mile after mile.
A DU professor dedicated his run to one of his students, Alex Teves, who was killed in the Aurora theater shooting.
Max Wachtel was Alex's forensic psychology professor at DU.
Wachtel said it's important for people to remember the names of those lost in the theater shooting.
"Around mile 21 that's when the marathon starts to get really hard," Wachtel said. "The course goes right by DU right where I teach and Alex took his classes. It felt great. It felt like he was there with me."
This was his way of keeping Alex's name in the minds of all.
(KUSA-TV © 2012 Multimedia Holdings Corporation)