Contrary to elite performance that is approaching an asymptote, recent analyses suggested a trend for improvement in veterans. This might be attributable to a disproportionate increase in older age-group participation. We extracted 26 years (1987-2012) of men's results of a running event in Switzerland, "La Course de l'Escalade" (7.25 km). We investigated trends in performance by five-year age-groups, taking the 10, 20, 30, and 50 fastest in each group, and then the 1 javax.xml.bind.JAXBElement@7a4092df , 5 javax.xml.bind.JAXBElement@7d5fdd15 , and 10 javax.xml.bind.JAXBElement@3ab34c0d percentiles. Taking the 10, 20, 30 or 50 fastest runners there was a trend for improvement ranging from 0.07 to 0.22 min·year javax.xml.bind.JAXBElement@2014a19 (p < .0001; 95% CI -0.083 to -0.049 and p < .0001; 95% CI -0.250 to -0.196 respectively) in the elder age-groups. Taking the 1 javax.xml.bind.JAXBElement@7c29e6ec , 5 javax.xml.bind.JAXBElement@7f9d2b09 , and 10 javax.xml.bind.JAXBElement@5feed3d3 percentiles there were no trends for improvement, and actual deteriorations up to 0.13 (p < .0001; 95% CI +0.119 to +0.138) min·year javax.xml.bind.JAXBElement@57371bb5 . Mixed-effect models with repeated measures for runners, confirmed a global deteriorating trend with an estimate of +0.11 min·year javax.xml.bind.JAXBElement@641a8939 (p < .0001; 95% CI +0.107 to +0.116). The results suggest that increases in performance in older runners arise from modifications of sampling from a growing population.