There is no question that completing a 5K is demanding on the body, especially when pushed to its physical limits. Determining the need to consume some form of calories while performing this distance will be dependent on reviewing specific energy demands, along with evaluating the duration and intensity of the run.
Primary Energy Sources for a 5K
Glucose (aka blood sugar) and glycogen will be the main energy sources for 5K performance. Glucose and glycogen are forms of carbohydrate produced during the digestive process. Glycogen is broken down into glucose to supply energy. The body is able to store a certain amount of glycogen in the muscle cells and liver, which allows for prolonged physical activity. Generally speaking, people will have enough glycogen to fuel working muscles for 90 to 120 minutes at a medium to moderate intensity. After you become depleted of glycogen, you will be forced to reduce the intensity and use fat as a primary fuel source.
The Role of Exercise Duration and Intensity in Glycogen Depletion
Although there is not 100 percent agreement within the exercise physiology community as to exactly what causes fatigue during exercise, the current theories revolve around energy depletion, psychological factors and certain changes in the central nervous system. In his book "Lore of Running," Tim Noakes reports that significant muscle glycogen depletion doesn't occur during a high intensity effort that last less than one hour. In fact, glycogen depletion will be the greatest after exercise that lasts a hour or more and that is done at a medium to moderate intensity.
Evaluating the Need to Consume Calories During a 5K
Knowing how much energy reserve your body has available and how long your event will last determines if you need to take in additional calories as you are going. In the case of a 5K, it isn't uncommon to see people in the front group complete the distance in 15 to 17 minutes. A majority of participants will be able to finish the task in under an hour. In "Food For Fitness," Chris Carmichael states that runners should plan on consuming some form of carbohydrate during competitions that will last an hour or longer. The purpose of this practice is to provide energy to your central nervous system and working muscles, thus saving your reserve of glycogen and preventing you from running out of fuel. An individual who puts forth his maximum effort throughout a 5K event will see very little benefit from dietary intervention because the duration and intensity of the performance will not lead to glycogen depletion.
Nutritional Suggestions
Certainly there are dietary considerations when preparing for a 5K. For example, consuming a proper diet from the 5 main food groups in the weeks and months leading up to any event will provide the body with quality nutrients that will be used for energy production. Although there isn't evidence that calorie consumption during a 5K will significantly enhance performance, it is accepted that this practice is useful for ultra marathon, marathon and half marathon distances.
References
- "Chris Carmichael's Food For Fitness"; Eat Right to Train Right; C. Carmichael, et al.; 2004
- "Lore of Running," Fourth Edition; T. Noakes; 2001
