Drink the day preceding the test and until sleep time to remain very much hydrated. One hour before work out, drink a low-portion sugar based beverage (20 g/l). Favor fructose to sucrose to dodge hypoglycemia because of insulin creation ( more data ).
During exercise, don’t stand by until you are parched to drink. The sensation of thirst shows a critical drying out (20% of the body’s requirements) that it is practically difficult to make up for lost time during the trip. Likewise note that our stomach can not ingest in excess of 75 cl of fluid for every hour. So drink routinely and in little amounts.