When you run a half marathon, you spend months training for the race. Much like the marathon, training is not the only factor for success in the half marathon. Your pacing strategy and race day fueling significantly impact your performance. How you fuel during a half marathon can help you have a breakthrough day – or at the very least, prevent you from ending in a struggling shuffle.
While you could complete a half marathon without fuel and not hit the wall, you would still likely fade. Who wants to fade in a race they spent months preparing for? To optimally perform in your race, you want to optimally fuel during a half marathon.
Why You Should Fuel During a Half Marathon
The half marathon is a long-distance race, like the marathon. Its duration means performance is dependent on adequate energy production. Without adequate substrate availability (ie fuel), you run out of energy and fade in that challenging final 5K. However, the half marathon is paced at a higher intensity than the marathon. For many runners, it falls right in the moderate-intensity zone, close to the lactate threshold (moderately hard) for advanced runners. At this moderate to moderately hard intensity, the body utilizes a greater percentage of carbohydrates than fats as fuel. You burn through energy, particularly carbohydrates, at a faster rate than you would covering the same distance at an easy pace.
The present body of research indicates that the half marathon is heavily carbohydrate dependent. In a 2016 study published in the Journal of Applied Physiology, the authors found that suppressing fatty acid oxidation did not impact half marathon performance. The researchers concluded this was because the runners relied almost entirely (~83%) on carbohydrates as the source of fuel for the half marathon.
As discussed in this post on marathon fueling, many runners could support 80 minutes of higher intensity running based on glycogen stores alone. However, the best researchers in sports nutrition argue this is not optimal for performance. According to a systematic review in Applied Physiology, Nutrition, and Metabolism, taking fuel during a half marathon maintains glucose levels in the bloodstream. The higher levels of plasma glucose lead to more carbohydrate oxidation in the working muscles, which means more energy is produced.
Finally, there is the aspect of delaying fatigue of the central nervous system. The receptors in our mouths stimulate a reward signal in our brains when we eat carbohydrates (particularly the sugars used in sports nutrition products). This reward signal gives the central nervous system a boost and improve performance.
How to Fuel During a Half Marathon
In some ways, fueling during a half marathon is similar to that of the marathon. You ensure your glycogen stores are optimal with a pre-race meal. Then, you want to supplement with carbohydrates (such as running gels or sports drinks) throughout the race. An optimal range of supplementation is 30 to 60 grams of carbs per hour during the race. For those taking longer than 2-2.5 hours, they may need slightly more.
Even faster runners (<90 minutes) should be mindful to ensure a high availability of carbohydrates before and during, according to the same study. The faster you run a half marathon, the closer you are working to your lactate threshold. This high intensity increases the rate of carbohydrate oxidation during the race. For slower half marathon runners (2.5+ hours), the fueling demands may even be closer to that of a marathon, as glycogen depletion becomes more of a concern.
Other than finish times, fueling guidelines will not differ significantly based on gender or bodyweight. Research indicates that body weight does not significantly affect carbohydrate oxidation. While women oxidize fat differently than men due to higher amounts of intramuscular triglycerides, the current body of research does not indicate that women need to fuel differently.
However, there are individual variations. The range of 30 to 60 grams of carbs per hour is quite large. Each runner will fall somewhere in this range, but where will vary. Observe: how do you feel during long runs? Do you feel fatigued near the end? Then you may need to fuel more.
Should I Carb Load Before a Half Marathon?
A carb load can be beneficial before a half marathon, especially if you anticipate the race lasting longer than 90 minutes. The carb load does not have to be as long as it would for a marathon. A one day increase in carbohydrate and fluid consumption can prepare you for the half marathon. (Here’s how to carb load effectively.)
What About Caffeine?
Caffeine can improve performance in endurance sports such as the half marathon by 2-4%. Caffeine reduces fatigue of both the central (brain/spine) and peripheral (extremities) nervous systems. Less perceived fatigue means you can continue to hold your pace for longer in the race.
In the central nervous system, caffeine binds to adenosine receptors and increases the density of the neurotransmitters. This physiological response reduces the perception of effort and central fatigue. Additionally, caffeine consumption can produce greater force production from the muscles. Caffeine increases the mobilization of calcium ions, which work within the muscle fibers to produce force. This effect delays muscle fatigue during running.
A recommended dosage of 3-6 mg of caffeine per kilogram of body weight, consumed approximately 60 minutes before the start of your half marathon. With this amount, dehydration should not be a concern, but you should still always be mindful to hydrate adequately. During the race, you can take gels with caffeine to provide a further boost. It takes approximately 45-60 minutes for caffeine to peak in your system. Time your caffeinated gels so that the peak coincides with the hardest miles of the race, rather than too early or too late.
However, some individuals experienced adverse reactions to caffeine that outweigh the performance benefits. Severe side effects of caffeine ingestion include anxiety, restlessness, elevated heart rate, heart palpitations, headaches, increased urge to pee, and gastrointestinal distress. If you experience these, you want to avoid caffeinated supplements on race day. Higher doses of caffeine produce more negative side effects. Some sensitive individuals can use a smaller dose, but some should forgo caffeine supplementation altogether. Caffeine response is based on genetics, not exposure. Always test caffeine in long runs and hard workouts leading up to your half marathon.
How to Fuel During a Half Marathon
Half marathon fueling leaves room for individual adjustments. Choose the race fuel that works best for you. Pick what sits best on your stomach for your pre-race breakfast. The goal of eating before and during is to have optimal energy with minimal GI upset.
- Prior to the race: Have a bland pre-race breakfast with a minimum of 100 grams of carbohydrates 2-4 hours before the race.
- Under 2 hours: 30-60 grams of carbohydrate per hour, at increments of 20-40 minutes
- Over 2 hours: 40-80 grams of carbohydrate per hour (similar to fueling a marathon), at increments of 20-40 minutes
You do not want to wait until race day to try your half marathon fueling strategy. Experiment in training during long runs. You want to practice for about six weeks or more before your race.