The aim of this thesis was to advance the methods of assessing laboratory based running performance and study the influence of carbohydrate-electrolyte( CHO-E) solutionso n self-selectedr unning speeds. The first study (Chapter 4) attempted to improve the methods used for treadmill timetrials by using an automated treadmill system that allows runners to rapidly change their running speed without engaging with the treadmill control panel. To this end, the study examined the repeatability of a1h running time-trial, in which the aim was to achieve the greatest distance in the set time. The coefficient of variation (CV), estimated using ANOVA with subject and trial as main effects, was 1.4%. Therefore, it was concluded that asking runners to cover as much distance as possible in 1 h, using an automated treadmill system is a reliable method of assessing endurance performance in endurance trained runners...