Fueling on the Run
This blog will explain in basic terms how the body uses fuel for running, what happens when we “bonk” or “crash” and how to avoid it.
Note: Fueling on the run is important even for runners in shorter distances who aren’t in danger of bonking. I will cover this in my next blog post: Fueling on the Run: Shorter Runs and Workouts. Stay tuned next week.
Carbs Carbs Carbs
Carbs, proteins and fats can all fuel our bodies. Where carbs can be digested quickly to provide fast energy, fats are digested slowly, and protein is not really meant to be a fuel source. The body will only break down protein for fuel if there’s no energy available from fat or carbs.
Our bodies prefer carbs while running because they offer fast energy (fuel that can be accessed quickly). There are 3 types of carbs (sugar, fiber, and starch) with sugar being the most simple form and therefore the quickest to digest and convert to usable energy.
In the body, glycogen is a carbohydrate that can be quickly be converted to glucose and pumped through the blood stream for fast energy.
Bonking / Crashing
The human body stores glycogen in muscles. Muscle glycogen is ready for quick conversion to glucose to use as fuel during hard/ intense physical activity. But our bodies cannot store a lot of glycogen, so the supply will run out during long runs, resulting in the dreaded “bonk” or “crash.”
Long distance runners will often carb load before a big race or run to maximize the body’s muscle glycogen stores. But as mentioned above, stored glycogen is limited. No matter how much we carb load, the muscle glycogen will run out if we run long enough without taking in additional carb during the run. That’s when we crash.
Note: even if we crash, there is still energy available as the body can burn fat and break down muscle for energy. But these are much slower processes.
How to Avoid the Crash
During a run, we want to spike our blood sugar. We want carbs that can be converted into glucose pumping through our arteries ASAP. There are lots of energy gels, chews, sports drinks designed specifically for this purpose, where glucose is the main ingredient. These are great options, very convenient, and eliminate a lot of guess-work.
To prevent bonking and delay the feeling of exhaustion, the goal is to consume simple carbs throughout the run. Even though simple carbs offer fast energy, it’s not instantaneous. That’s why it’s important to start fueling as early as 5km or 3miles into a long run or race — before starting to feel weak or hungry, and continue to fuel throughout your run.
To dial in on your individual needs or for more information of any of these topics, I highly recommend consulting with a Registered Dietitian.
Nicole Sifuentes is a full-time Running Coach for adults of all ages and abilities. She is a former professional runner and 2-time Olympian, and Certified Strength and Conditioning Specialist. Read more about her services, and schedule your free coaching consultation.