I thought I would share this abstract -
http://www.ncbi.nlm.nih.gov/pubmed/21590642"Further covariate-adjusted analysis revealed that those competitors who consumed carbohydrate the day before the race at a quantity of >7 g/kg body mass had significantly faster overall race speeds (P=0.01) and maintained their running speed during the race to a greater extent than with those who consumed <7 g/kg body mass (P=0.02)."
Obviously, conclusions from studies such as these should be taken with a grain of salt. But I thought it was interesting!