Race Strategy – Fluids and Carbohydrates

Strategic Questions

If you are training for an event that will last longer than 60 minutes, then you should be asking yourself these questions. What energy sources will you rely on to keep your energy level sufficient to avoid bonking during your event? What fluid sources will you rely on to keep yourself sufficiently hydrated so you will keep your body temperature under control and compete well in your event? What electrolyte sources will you rely on to keep your muscles contracting and your stomach emptying properly during your event? Should you be experimenting during your training season to determine what you can eat and what you can drink during the race without getting sick to your stomach? Our recommendation is to not wait too long into your training season to begin experimenting with fluid, fuel, and electrolyte replenishment. It takes time and trial and error to figure out the right combination and amounts that best suit your purposes.


When discussing event-day strategic consumption of fuel (primarily carbohydrates), fluids, and electrolytes, we begin with the assumption that you have sufficient and balanced nutrition and adequate hydration as a lifestyle. If you aren’t practicing these good daily and weekly habits, you need to know you can’t fix everything just by doing things right on event day.

Energy Stores in Muscles, Liver and Bloodstream

A flat half-marathon is going to take most people anywhere from a little less than two hours to three plus hours. The human body is capable of storing no more than 120 minutes worth of energy (glycogen – glucose in its stored form and it comes primarily from complex carbohydrates) for running in the muscles and liver and this is only if you saturate yourself with it in advance. Since most people can’t run a half-marathon under two hours and many won’t make the effort to maximize their glycogen stores in advance, they will need to supplement with additional carbohydrates during the event. By the way, if you strictly run and don’t mix running and walking, your body will restrict your access to body fat stores as a fuel source after the first few minutes, until you finish or deplete your glycogen stores. This happens because running expends energy at a rate faster than our brains are comfortable with. This protective mechanism is designed to ensure we have body fat stores to sustain us if, for any reason, we stop eating sufficiently.

Assumptions and Calculations

Assumptions: If a woman weights 130 lbs. and can run a half marathon in 2:30, she will need approximately 1,300 calories (about 520 calories per hour) or approximately 100 calories per mile to complete her event with sufficient energy. With proper training and race-week and day fueling strategy, she will likely start the race with about 1,000 calories of glycogen reserves in her muscles, liver, and bloodstream. Calculation: this woman will need to consume about 300 calories during the half marathon to avoid bonking.

Questions Needing Answers

What sources and quantities of carbohydrate should you consume during the half marathon? How much fluid and what types should you drink? What about electrolytes? Should you start experimenting early in the season by treating each long-distance workout as a dress rehearsal for event day?


Through effective training with BOISE RunWalk’s training program, you have arrived at the starting line with a proven plan and the confidence that you will have lots of fun running your half-marathon. You now have a plan that will work for you. You learned what complex carbohydrate source best built up your glycogen stores and how much to eat. What source of carbohydrate during your event did you settle upon? What sports drink did you test and find worked best as a source of fluids and electrolytes? Are you eating chicken sandwiches and pretzels every other mile during your race? Whatever you have decided, you arrived at your decision by experimentation, treating each Saturday morning as a dress rehearsal for race day. Yes, you likely made some mistakes along the way, especially early on, and things sometimes might have gotten to be a little messy. But by mid to late-season, you were fine-tuning your decisions as to the sources of carbohydrate, fluids and electrolytes. And your BOISE RunWalk coaches were very helpful, by providing an example chart showing carbohydrate and fluids consumption for three difference race finish times. See example chart above (note: W=water, PA=sports drink PowerAde, G=Gu).