Running on fumes: When and why to do depletion runs
Running in a semi-starved and carb-depleted state can train the body to become more efficient at using plentiful energy sources like fats
While breakfast continues and will always be the most important meal of the day, there is indeed a time and place to hold off on the cup of coffee and skip the cereal.
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Depletion running is the name given to runs that are done in a semi-starved or depleted state. Most predictably, this occurs in the morning immediately following a full night’s sleep. This means that many hours have passed since your last meal and is when glycogen–the body’s stored carbohydrate source for energy–is at a minimum.
The basic idea behind a depletion run is to train the body to use alternate fuel sources, such as fat, when it’s preferred fuel of carbs is in short supply. This is particularly important for distance runners who find themselves with limited glycogen near the end of a long run or race such as the marathon.
The more efficiently a runner is able to use fat stores for energy–which exist in a nearly endless supply–the longer they’ll be able to maintain their pace in a long race and arrive at the finish faster. Depletion runs train the body to both use its available glycogen more efficiently and also to use fats when glycogen levels are low. They may also impact (increase) how much total glycogen our body is able to create and store which then becomes available the next time we need it.
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A popular approach is for runners to train and in a near depleted state and race in a fully carb loaded state when glycogen stores are highest.
In general, it’s probably best to save depletion runs for easy recovery running and not for a hard workout or long run. Good options are to do a recovery run on the morning following a long run or the morning following a hard workout.
Be warned however that these types of runs are physically and mentally tough, especially for the first few times. You may notice feeling slow, sluggish, tired or just plain awful on a depletion run. Remember that these runs are not about speed or pace, but simply about covering distance and logging time in an already depleted state. In time, they should feel better as your body adapts and will also contribute to performance gains.