Intra-Race Fueling

Intra-Race Fueling for Marathons
from Laine Greenawalt at Case Specific Nutrition

Blocks, Gels, and Sports Drinks - How to use them to fuel your race

With physical activity, the body has an increased reliance on carbohydrates for fuel. Carbohydrates serve as the main energy source for skeletal muscle, and allow them to continue to contract under the stress of exercise. For this reason, intake of carbohydrate foods should match activity level. For example, as exercise intensity and/or duration increase, so does carbohydrate demand. Pre-, intra- and post-race fueling are critical for sustained performance, adequate recovery, and injury prevention.

During exercise, the cardiovascular and respiratory systems are in a state of stress, trying to deliver adequate oxygen to the muscles. As oxygen demand increases, energy needs also increase. The body derives the needed energy mainly from carbohydrate stored in the muscles and liver in the form of glycogen. As carbohydrate stores are depleted, the body begins looking for other fuel sources, namely fat and/or protein (this is “hitting the wall” or “bonking”). However, the process of converting of fat to a form of usable energy is slow, and mid-run your body will be unable to meet increased energy demands. This leads to increased fatigue, increased rating of perceive exertion, and a declining performance. The goal of proper sports nutrition is to prevent this depletion of fuel stores at the corresponding decrease in performance.

Proper fueling will allow you to maintain your predetermined pace for the entire race. For runs lasting <90 minutes, it is unlikely that your body will need any intra-race fuel and will perform well with an effective pre-workout meal. However, if you are exercising for >90 minutes, intra-race fuel (calories consumed during a race) will be necessary to maintain performance. During exercise of this duration, carbohydrate stores will be depleted before reaching the end of the race, so it is important to overcome this with small, intra-workout feedings. Intake of simple carbohydrate is needed to maintain blood sugar, preserve energy stores, and continue delivery of fuel to the brain. This is where items like sports drinks, gels, beans, etc. come in handy.

Half-Marathon: It is unlikely that you will need intra-workout fuel for a half marathon. The race is not long enough to completely deplete carb stores. However, if you are working at a higher intensity (greater than moderate exertion), some carbohydrate may be necessary, but it won’t take much (15-30g). 8-12 ounces of a standard sports drink or one Gu Energy Gel will be plenty to keep your energy levels up and your race going smoothly. If you are planning to include fuel into your half-marathon, consider having it between miles 7-9. We are trying to prevent a decline in energy, so it is best to consume them before you crash.

Full Marathon: If you are planning to run a full marathon, intra-race fueling is inevitable (unless you are following a ketogenic diet, but that’s a topic for another day). The body’s carbohydrate reserves are simply not large enough to last the full 26.2 miles, even with proper carb-loading and pre-workout fueling. At this point, glycogen stores are becoming depleted and need to be preserved for as long as possible. Small servings of simple carbohydrate in the range of 20-30g is best. Here are some common options:

  • 5-6 dried apricots
  • 3/4 cup dry cereal
  • 10oz sports beverage
  • 1 Sports Gel
  • 1 serving sport beans or blocks

Rule of Thumb: Pack what pleases your tongue and your stomach!

Fueling needs vary by individual depending on level of training, pace, and fitness level, but generally the first feeding should occur between miles 8-10. After the first feeding, timing depends on the intensity level and your individual calorie needs. A large male running at a moderate intensity will need significantly more carbohydrate than a smaller individual running at a lower intensity. Typically feeding points are:

  1. Mile 8-10
  2. Mile 13-15
  3. Mile 18-20
  4. Mile 22-24


Since we know we will need carbohydrate, testing the source and timing during training is crucial. Using a variety of sources may keep your palate interested, or maybe you prefer to stick to one type of fuel. Different protocols work for different people. The ultimate goal of intra-workout fueling is to consume simple carbohydrate, low in fiber, that are convenient to carry and swallow. It is best to test a couple options during training. Once you exceed 10 miles in training, you can begin adding a carb source and asses how your body feels. Plan your feedings ahead of your decline in performance by starting conservatively and listening to your body.

Overall, intra-race fueling is not complicated but it is individual. Other important factors to consider include: pre- and post-workout meals as well as proper hydration. For more details on your personal needs, contact a sports dietitian to help you develop a plan for optimal performance!

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