A stated purpose of sports drinks, which provide many calories of energy from sugars, is to improve performance and endurance. In an analysis by Matthew Thompson and colleagues from the Oxford Centre for Evidence Based Medicine, of 431 marketing claims of performance enhancement, most cited no evidence. 174 sources were cited for GlaxoSmithKline's Lucozade; of them, Thompson found only three studies of high quality with a low risk of bias. The rigorous studies that did show improved endurance were "of limited relevance to most people because the tests were on elite athletes". Thompson said that, for the vast majority of people, drinking such products "could completely counteract exercising more, playing football more, going to the gym more".