What Is Bonking? And How To Avoid It

If you want to avoid hitting the wall, take a look at your nutrition, training, and race plan.


When runners and other endurance athletes talk about “bonking” or “hitting the wall,” they are referring to the depletion of glycogen stores found in the liver and muscles after longer periods of exertion (like a marathon or ultra like the Two Oceans). Most people who have done a marathon or more know what bonking feels like — you’re having a great run when all of a sudden at the 32K, BAM, those hamstrings or other muscles seize up, energy plummets and you’re ready to consume any food to return to normal.

Because glycogen fuels a runner’s energy production as they are exercising, when it’s drained you will experience sudden fatigue and that loss of energy. It is often accompanied by muscle cramps, GI distress, and/or mental confusion. Bonking is basically a complete shutdown of all of the body’s systems.

It is suspected that as glycogen stores get low, the brain sends out signals to shut everything down in an attempt to save itself.

Because glycogen is derived from the foods we eat, you need to look at your nutrition when trying to figure out how to avoid hitting the wall in races or on regular runs. To help you overcome the bonk, we’ve narrowed things down to help runners perform better when it comes to nutrition and their preparation before a big race.

Nutrition to Beat Bonking
Your daily diet should include adequate carbohydrate intake, which for most runners is about 60 percent of their daily kilojoules. Carbohydrates include all vegetables, fruits, legumes, breads, pastas, rice, grains, and even dairy products. With the increasing interest in cutting out wheat and processed foods, it’s important to make sure you are still consuming adequate carbs if you are eliminating them from your diet.

Four days before your race, increase your carbohydrate consumption to 70 to 90 percent of your diet to make sure you are fully loaded for your event.

After exercise, muscle cells are primed to absorb nutrients at a faster rate than normal. Picture a dried-out sponge (your tired muscles) being dropped into a bucket of water (nutrient-rich blood). What happens? The dried-out sponge quickly plumps up and becomes saturated and pliable — just what you want your muscles to experience after a run. Therefore, it is very important to eat within 20 to 30 minutes post-run. After 45 minutes, muscle sensitivity to insulin declines, slowing down the absorption rate. Get into the habit of packing a carbohydrate-protein-rich snack to bring with you to eat or drink after every run. (Low-fat chocolate milk is a good, easy one.)

Taper Right to Beat Bonking
Tapering is essential for a successful race and to counter that depletion that can lead to a bonk. For the unfamiliar, tapering refers to reducing the volume of your weekly mileage during the final two to four weeks leading up to the marathon. The purpose of the taper is to minimise fatigue, rather than to attain further physiological gains. Studies have shown that tapering allows muscle glycogen stores to return to peak levels before the big run. Muscle and connective tissues can repair and strengthen, and the body’s immune system shows dramatic improvement.

One study found that subjects who tapered properly improved their marathon performance by an average of 3 percent, which can translate to five or 10 minutes!

Fuel During Your Race to Beat Bonking
Don’t skip that morning breakfast before a big race. During the night, your glycogen levels will drop slightly because the body is still working and using energy, so you wake up with a slightly empty tank. Also, wake up early so you can eat three to four hours before a longer race. Consume between 800 and 1500 kilojoules depending upon your size and the length of your race. Remember that you may need to experiment to find what works best for you in the am, but some standards are a toast with peanut butter, water and sports drink.

We suggest if you’re running for over an hour, make sure you consume about 30 to 60 grams of carbs every hour. You can get that from gels or chews (or whatever works best for you… just make sure you practice it during training.) Supplement your food intake with sports drink and/or electrolytes because it’s important to maintain the osmotic pressure among cells to prevent dehydration. Even a very low level of dehydration will facilitate bonking because it slows gastric emptying, which means nutrients are not going to make it into your bloodstream. Even a sip of water every 10 minutes can be helpful.

Your GI system becomes compromised on race day, which does not work in your favour. First, race anxiety reduces some of the blood flow to your gut as the body prepares to run.

And second, blood flow is diverted from the gut when running and redirected to working muscles to provide them with much-needed nutrients and oxygen, leaving our digestive capabilities compromised. By putting water, sports drink, and some nutrition in your gut, you’re forcing it to keep blood flow there, making it stay open and functioning.

Also, begin race-fueling early on. You can take smaller amounts of fuel to avoid GI distress, but by taking it early and more frequently, you keep this system working.

Another pro tip: Stay aware of how you are feeling mentally when running. Mental fatigue leads to the perception of muscular fatigue. If the brain thinks things are not going well, it begins shutting down all systems. Carry some special treats with you, look for an encouraging sign on the course, or listen to your favourite music to get out of your funk.

READ MORE ON: HITTING THE WALL marathon tapering marathon training nutrition race day

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