Ulrich Kamm, 60, Debbie Richmeier, 47, and Glen Turner, 48, have outlasted 10 other competitors who began the marathon at 5 p.m. Friday and said they plan to continue walking Tuesday until they break the world record for marathon walking, a feat that would be accomplished at about 11 p.m., The Boulder Daily Camera reported Tuesday.

Participants in the "Extra-Mile Endurathon," which is part of a string of similar events scheduled around the world this year, must remain walking day and night with only 10 minute breaks every four miles. The last walker standing will win a $1,000 if he or she walks at least one mile past where the second-to-last competitor calls it quits.

The last four walkers from the Endurathon, as well as the final four from competitions in Buenos Aires, Berlin, Paris and Tokyo, will be invited to compete for $100,000 in Las Vegas.