Some old tricks really do work. Loading up on carbohydrates the day before a race can help you maintain your pace, a new British study confirms. Optimal amount? London marathoners who ate more than 3.2g of carbs per 450g of body weight the day before the race finished faster and at more constant speeds than those who ate less. Carb loading preserves glycogen – the fuel in your muscles and liver, says study author Dr Greg Atkinson. Vary your sources: try raisins, cereal, potatoes and pasta, he says. Here are 5 Carb Secrets to give you a boost.