The Next Loop Endurance Series - Lake Carl Blackwell
Lake McMurtry, United States • 21 Nov 2026
The Next Loop Endurance Series - Lake Carl Blackwell: 40/50 Mile Challenge
The 40/50 Mile Challenge is a continuous loop endurance race held at Lake Carl Blackwell in Stillwater, Oklahoma. Runners complete repeated laps of a 3.1-mile (5K) loop until they reach their chosen distance or the event time limit of 12 hours. Distances offered are 40 miles and 50 miles, and competitors are scored separately from the hourly Next Loop Endurance Series participants.
The course loops through rolling lakeside terrain, open grasslands, and wooded sections, and it returns each lap to the same central start and finish area. The trail surface is a mix of dirt paths, grass, and lightly packed earth. Gentle rolling elevation and several wide sections provide generally good footing for repeated laps.
Support and logistics include a fully stocked aid station at each lap and designated personal staging areas near the start and finish where runners can access their supplies each loop. Crew access is permitted in designated areas, pacers are allowed per event rules and timing conditions, and medical and race staff are on site throughout the event. The continuous loop format emphasizes consistent footing, centralized support, and simplified logistics for pacing and refueling. Visit the organization's website for the most recent information.
- 40 Mile
- 50 Mile