As runners, understanding how our body stores, processes and uses glycogen is crucial as it increases and maintains our energy levels which can improve our performance and make sure we make it to the finish line.
Glycogen is a branched polymer of glucose stored in the liver and muscles and is a source of fuel for exercise. Glycogen metabolism is the process of how these stored carbohydrates are used as fuel, which involves many enzymes with chemical compositions. Basically, excess carbohydrates are stored as glycogen in the liver and muscles, turning your “carbohydrates food consumption” into performance.
Our body has access to two sources of energy fuel while running or exercising. Glycogen is the main source of energy for moderate to high-intensity training, while fat burning is another source of energy used mostly during low-intensity efforts. Low-burning fat energy takes too long to process to fuel sustained moderate to high-intensity efforts. Both energy sources are important for running, especially long-distance running.
Carbohydrates storage and burning:
Our body can store an average of 300-400g of glycogen when fully fueled, while it will burn an average of two to three grams of carbohydrates/minute at moderate effort (120g-180g/hr). This storage versus burning equation will sustain about 90-120mins of intense training. Glycogen burns rapidly, but post-exercise it will replenish at a rate of 2%-5%/ hour. When our body is completely depleted of glycogen it can take a full day or more to replenish. That is why looking after our nutrition pre-training, during and post-training is so important.
Glycogen replenishing while running:
Imagine if a runner can store an average of 350g of carbohydrates as glycogen, can replenish 60g/hour while burning 180g/hour, with no carbohydrates the runner will bonk after two hours. For long runs, the key is to reduce the amount of carbohydrates burned per hour by reducing the intensity level so the body can burn more fat. The solution; pace yourself to achieve the optimal fat-to-carbohydrate burn rate to avoid bonking. For races less than two hours you can go hard, for races 2hrs-3 1/2hrs go moderately hard rate, go moderate for races 3 1/2hrs- 5hrs (fat burning becomes more important) and for ultra-distance go easy-moderate pace. For runs longer than 60-90mins make sure you focus on refueling as you go, consuming 200-300 calories/hour of mostly carbohydrates (banana, gels, sport drinks, energy bars). For ultra-distance runs, it is important to consume some easy to digest food, including low amounts of protein, at some points is also crucial to support our muscles. Not consuming enough carbohydrates and some protein during ultra-distance runs will cause low glycogen stores, fatigue and even lead to “catabolic” state, involving muscle breakdown by requiring the body to rely on protein and amino acids for fuel. Looking after our nutrition pre-run, during and post-run will increase our performance and recovery during and post-race.
Train Hard, Eat Right, and Feel Great!