Iowa State University Veterinarian Records, RS 22/6/0/9, University Archives, Special Collections Department, Iowa State University, http://www.add.lib.iastate.edu/spcl/arch/rgrp/22-6-0-9.html
Perhaps the greatest tests of a horse's athletic ability and "heart" are the long distance trail ride competitions and combined training events. In no other equestrian competition is a horse's endurance and stamina so challenged. Long distance trail rides are generally grouped into two classifications: competitive and endurance rides. In competitive trail rides, horse and rider cover from 25 to 100 miles in one to three days, depending on the specifications of each ride.
Dwyer, Roberta M. and Thompson, Linda S.
"The Practical Diagnosis and Treatment of Metabolic Conditions in Endurance Horses,"
Iowa State University Veterinarian: Vol. 47
, Article 3.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol47/iss1/3