Sehovic, E., B. Knechtle, C. A. Rüst, and T. Rosemann. “12-Hour Ultra-Marathons: Increasing Worldwide Participation and Dominance of Europeans”. Journal of Human Sport and Exercise, vol. 8, no. 4, Dec. 2013, pp. 932-53, doi:10.4100/jhse.2013.84.05.