Before I start, I am not a nutritionist but I do have experience of being around professional athletes so this is more what I’ve seen than what I’ve researched.
Athletes tend do load on carbohydrates before competing. Some of these are simple carbohydrates because they contain very few molecules, which means they break down quickly and you get the energy quicker. This includes some sweets like wine gums and jaffa cakes – I’ve seen footballers eating these at half time.
Complex carbohydrates tend to be eaten about 3 hours before competing. These include rice (brown rice is best), pasta… that kind of thing.