Scientific papers and Journal articles on the System
Hugo, M.L. 1998: Difficulty Grading of Hiking Trails. Journal for Research in Sport, Physical Education and Recreation. 21(1) : 47-54 (With Kruger,P.E., Jansen van Vuuren,T.B.R. and Hugo,M.L.(jnr).
Hugo, M.L 1999: Energy Equivalent as a measure of the difficulty rating of hiking trails. Tourism Geographies 1(3):1-15
Hugo, M.L 2000:A Comprehensive Approach towards the Planning, Grading and Auditing of Hiking Trails as Ecotourism Products. Current Issues in Tourism (lead article) 2(2 & 3):124-136
Hugo, M.L 2000. Grading of Trails. Sustainable Tourism. Papers collected from the 98’ International Geographic Union Study group Meeting. Lisbon. (pp.166-177).