The Science Of "Bonking" And How To Avoid It On Race Day

During an endurance event, the energy requirements demanded from your body are somewhat extreme. Bonking often referred to as “hitting the wall”, is an unfortunate but common race-day phenomenon that occurs when carbohydrates and amino acids get completely depleted from your body. Tanking during race day is exactly what you don’t want to happen, so we will discuss what bonking is its symptoms, and how to avoid it so you can finish your race strong from start to finish.

What Is Bonking

In recent years, participation in endurance events and ultra-endurance events, such as marathons, triathlons, and Ironman’s have increased worldwide, with nearly 4 million participants each year.

Ultra-races which last between 4-6 hours on average, exert a tremendous amount of fatigue on your body and require more physical demand. Suboptimal nutrition strategy going into race day, can leave you in a severe energy deficit and lead to tanking before the finish line and hitting the dreaded bonk.

Bonking is a relatively well-known phenomenon, often referred to as hitting the wall. The reason why you bonk, is due to low blood sugar (hypoglycemia). You can also experience what is called central nervous system fatigue, from a lack of amino acids, feeling as if you want to curl up in a little ball and take a nap on the side of the road.

What Are The Reasons For Hitting The Wall

Your body relies upon a continuous energy supply of glycogen derived from carbohydrates. This is the reason why at race stations, they give you fast-acting sources of carbohydrates made of sugar and maltodextrin such as energy gels, chews, energy bars, and Gatorade, which can provide more muscle fuel and energy and extend your time to exhaustion.

Unlike fat reserves, your body can only store a limited supply of glycogen within your muscles and liver, which ranges between 75-100, and 300-500 grams. You need upwards of 800 grams of carbohydrates during an ultra-endurance event making it essential to refuel along the way for optimal energy levels.

When you deplete your glycogen stores, you may experience extreme fatigue, sudden loss of energy, mental fogginess, and cramping; these are the symptoms of bonking and you are hitting the proverbial wall. Essentially your entire body and brain shut down and go into triage.

How To Avoid Bonking and Hitting The Wall


The best way to avoid bonking is by optimizing your nutrition protocol. Performance relies upon your nutrition and supplementation, not just your training. Without the proper fuel in your body, you won’t be able to perform at an optimal level.

Carbohydrates are the priority when it comes to distance and endurance training. Carb loading is an common nutrition strategy that will help glycogen resynthesize, and ensure you are good to go the following day.

Carbohydrate metabolism (as blood glucose and muscle glycogen) has the advantage of generating more adenosine tri-phosphate (ATP) per volume of oxygen (O2) compared to fat [R].

Academy of Nutrition and Dietetics (AND), Dietitians of Canada (DC), and the American College of Sports Medicine (ACSM) recommends Ultra-endurance athletes with extreme levels of commitment to daily activity (4–5 h of moderate to high intensity exercise every day) may need up to 8–12 g/kg/day of carbohydrates for optimal energy output and glycogen stores [R].

We recommend using a fast-absorbing carbohydrate supplement, such as Clean Carbs to help with prolonged endurance activity. Clean Carbs contains sweet potatoes, yams, oats, and blueberries to help sustain long-term energy and different releases times of glucose and insulin, for more energy and better performance.

However, studies show that even when glycogen stores are completely depleted after 4.5 hours of exercise output at 70% maximum oxygen consumption, endurance athletes can still run at 16km/hour for an additional 2.5 hours at 66% of their VO2 max [R].

Hitting the wall and bonking are determined, by more variables, than just carbohydrate depletion.


Electrolytes are crucial not only to avoid bonking, but for any type of workout for adequate and efficient hydration. Hydration during your workout is essential to prolong endurance activity, improve workout volume, delay muscle fatigue, and improve recovery.

Electrolytes are minerals and vitamins that conduct electrical activity in the body so that you can perform mechanical functions, such as muscle contraction and relaxation, which are a part of daily and athletic functions. With just a 1-2% reduction in body weight from fluid loss alone, performance takes a dive and perceived exertion goes plummets. In a typical workout, you can lose anywhere from 2-6% of your body’s water weight just by sweating. In an ultra, you can count on losing much more than that. The loss of water and electrolytes, coupled with not replenishing them, effects recovery times, oxygen levels, and nutrient deliveries contributing to muscle wasting and a poor removal of waste from the blood stream [R].

Electrolytes such as magnesium, potassium, salt can help replenish hydration. Coconut water is also a great ingredient for hydration. Naturally low in sugar, coconut water boosts the electrolyte potassium along with a few other nutrients.

RELATED ARTICLE 10 Symptoms Of Electrolyte Imbalance

Sodium and electrolytes help your body retain water, which is important during a race. If you don’t have enough electrolytes, your body will essentially stop working. Your legs will get heavy, you’ll feel extreme fatigue, and the dreaded wall will be waiting. You’ll need between 300-600mg of sodium per hour and if you’re a salty sweater, your intake is going to be higher than that. The International Society of Sports Nutrition recently recommended that ultra-endurance athletes should aim for between 450 and 750 mL per hour for adequate hydration [R].

Essential Amino Acids

To avoid hitting a wall, your body also relies on essential amino acids. Often referred to as the building blocks of protein, when protein is metabolized, it’s broken down into its simplest form amino acids. There are 20 common amino acids that play numerous roles within your human biology and 9 are considered essential. Amino acids are composed of an amino group and a carboxyl group which is acidic, hence the name amino acid.

Essential amino acids cannot be produced by your body, therefore it is “essential” to obtain them from the foods you eat or from supplements. Nine of the twenty amino acids are categorized as essential. Each amino acid, is separately, or in combination responsible for various functions in your body. Tryptophan, for example, is used to make niacin, melatonin, and serotonin, which promote healthy sleep and a positive mood state, while leucine is part of the branched chain amino acids, which helps stimulate muscle protein synthesis.

When your body works harder and harder during strenuous physical activity, muscle tissue is broken down, resulting in increased levels of tryptophan. Increased levels of the sleep-inducing amino acid tryptophan, triggers an increase in serotonin, which produces lethargy, decreases muscular contractions, and depresses motor neuron excitability.

A bonk happens when your body runs out of carbohydrates. However, when you demand more from your body, you need more fuel to supply it with, as it utilizes more resources. Your body doesn’t just use glycogen, it also uses electrolytes, water, fat, and protein.  

During high-intensity and prolonged endurance activity, you may experience an amino acid deficit, which leads to neurotransmitter imbalance. We call this muscle catabolism. Muscle catabolism takes place, when your body uses your muscle mass for energy, in times of severe nutrient depletion. When this takes place, you may also experience what’s called central nervous system fatigue.

For your nervous system to synthesize amino acids, you also need an adequate intake of b-vitamins which are also the primary building blocks of neurotransmitters.

Ingesting essential amino acids each hour during a race, will help you amplify your resistance to mental and muscle fatigue. I suggest supplementing with Swolverine’s INTRA. INTRA is a combination of essential amino acids, B-Vitamins, electrolytes from pink Himalayan salt and coconut water, as well as raw superfoods proven to help endurance, and recovery such as pomegranate, spirulina, and tart cherry extract.

What Is Bonking And How To Avoid It: Takeaway

Your nutrition is one of the most important parts of your training program. Without the right performance nutrition protocol in place, your chances of experiencing the bonk will be much higher and ultimately inevitable. Longer and more intense training sessions demand more fuel, hydration, and nutrients from your body. You can avoid bonking by making sure your amino acid, electrolyte, and carbohydrate intake is good before an endurance event. Focusing on amino acids, electrolytes, and carbohydrates is essential for adequate glycogen replenishment, muscular contraction, and maintaining a positive amino acid balance during race day. 

The Best Supplement To Avoid The Bonk, Is INTRA Workout Supplement From Swolverine

INTRA is an advanced intra-workout supplement made to maximize hydration and improve training performance during your workout. INTRA is made with proven sports performance ingredients, antioxidant-rich superfoods, and electrolytes. INTRA combines essential amino acids, tart cherry extract, pomegranate, spirulina, coconut water, and Panax ginseng for maximum endurance, mental focus, muscle growth, hydration, and recovery. Take your performance to where it's never been before with INTRA.

SWOLVERINE is an endurance athlete and active lifestyle brand. Made for the elite athlete, and the strong-willed our products were designed to fuel your athletic performance. We perform when you perform. 

We believe that everyone can optimize not only their athletic performance but their human potential. The way we believe we can optimize performance is through transparency, clinically effective doses, and clinically proven ingredients with evidence-based outcomes. We provide the nutrients you need to power your active lifestyle.

Walter Hinchman

Walter Hinchman

Walter Hinchman is the Founder and CEO of Swolverine. He is a NESTA and ACE certified trainer and holds a Masters Degree in Business and in Finance and Economics.


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