by Competitor.com, Published Aug. 29, 2014, Updated Jan. 18, 2016 at 12:29 PM UTC
Want to see what your made of? Test your mettle in one of these crazy-hard races!
Start your FREE subscription to Competitor Digital today!
Get our monthly digital magazine, weekly running content & exclusive offers delivered to your inbox.
© 2014 Competitor Group Inc. All Rights Reserved