As you gradually build to match the distance of your race, you should also train for how to fuel and hydrate your body during that distance.
If your race is under 60 minutes and you fuel and hydrate properly beforehand, you will not necessarily need to take in any more calories or fluid while you’re running. If you are training for a longer effort, however, it will be key to use your training runs to practice consistent fueling and hydration. Additionally, it’s always a good idea to know what food and hydration products will be offered at aid stations on the course and, if possible, train with those products; this information is usually available on race websites.
During your longer training runs, get on a consistent fueling schedule by setting your watch timer for 20-30 minute intervals at which you take in calories and hydrate; you can either use this same strategy during your race or just plan on stopping at regularly spaced aid stations. Practicing race day nutrition during your training will also allow you to fine tune the amount and type of calories your body can handle while running. You should generally aim on consuming 120-360 calories (30-90g of carbs) per hour of running, the exact amount dependent on duration, intensity and training.
In addition to figuring out how much to eat, figuring out how much to drink is also something to work on in advance of your race. Essentially, the goal is to replace what is lost through sweat, so run hydration should be about both fluid and electrolyte replacement. A good first step, and something you can do at home, is to determine your sweat rate or the amount of water lost via sweat in a given amount of time (typically an hour). For the specifics on how to effectively do a sweat test, visit Gnarly. When measuring sweat rate, it’s important to replicate the conditions you will experience on race day as closely as possible.
Taking in the right amount of water will get you halfway to properly hydrating, but if that is all you do, then your performance will suffer and you could seriously injure yourself. The other half of the equation involves replenishing the electrolytes lost in sweat. Determining the amount of electrolytes lost in sweat requires a sweat test which can be administered and analyzed in performance labs. Much like sweat rate, the electrolyte content of sweat is dependent on many factors and can vary greatly from person to person. Although sodium, potassium, calcium and magnesium are all lost in sweat, sodium is, by far, lost in the greatest concentrations, with losses ranging from 200-700mg per 16 oz of sweat. By choosing a hydration beverage that contains electrolytes at effective levels, you ensure you’re giving your body both the water and electrolytes it needs to perform optimally, while preventing cramping and dehydration.
