Gastrointestinal symptoms in long-distance runners, cyclists, and triathletes: prevalence, medication, and etiology. - Peters,H.P.F.; Bos,M.; Seebregts,L.; Akkermans,L.M.A.; van Berge Henegouwen,G.P.; Bol,E.; Mosterd,W.L.; de Vries,W.R. (Am J Gastroenterol, 1999)