During an endurance event, your body’s energy demands can reach extreme levels. One of the most dreaded experiences for endurance athletes is bonking, also known as “hitting the wall.” This occurs when your body completely depletes its carbohydrate and amino acid stores, leading to sudden fatigue, brain fog, and even muscle failure.
Tanking during race day is exactly what you don’t want to happen, so in this guide, we’ll explore what bonking is, its symptoms, what causes it, and most importantly—how to prevent it with proper endurance nutrition and supplementation.
What Is Bonking?
In recent years, endurance and ultra-endurance events—such as marathons, triathlons, and Ironman races—have surged in popularity, with nearly 4 million participants annually worldwide. These events often push the human body to its absolute limits.
The Science Behind Bonking And "Hitting The Wall"
Bonking is a physiological condition caused by severe hypoglycemia (low blood sugar) and a lack of amino acids, resulting in both physical and mental collapse. During ultra-races that last between 4–6 hours or more, the body uses up its limited glycogen reserves and essential nutrients.
"Bonking occurs when muscle glycogen is depleted and blood glucose levels drop, resulting in reduced central nervous system activity and performance failure." – Jeukendrup, Asker E., Sports Medicine, 2014
Read the study
What Causes Bonking or “Hitting the Wall”?
Your body primarily relies on carbohydrates for energy during endurance training. While fat is an excellent energy reserve, it is not as efficient as carbohydrates at producing energy quickly.
Glycogen Limitations
Your body can only store about:
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75–100g of glycogen in the liver
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300–500g in muscles
In ultra-events, you may need upwards of 800g of carbohydrates to sustain energy. Once these glycogen stores are exhausted, your body essentially goes into triage mode.
"The depletion of glycogen stores causes sudden fatigue, mental fog, and performance decline—classic symptoms of bonking." – Cermak, Naomi M., Journal of Applied Physiology, 2013
Read the study
How to Avoid Bonking and Finish Strong
Avoiding bonking requires strategic fueling, hydration, and supplementation before and during your endurance event.
1. Prioritize Carbohydrates
Carbohydrates are your main source of energy for endurance events. Carb loading before race day and consuming fast-acting carbs during the event helps maintain energy and delay fatigue.
Recommended Intake:
"Ultra-endurance athletes may require 8–12g of carbohydrates per kg of body weight per day to maintain optimal energy and glycogen stores." – Thomas, D.T., Journal of the Academy of Nutrition and Dietetics, 2016
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Product Tip: Swolverine’s Clean Carbs delivers complex and fast-digesting carbs from sweet potatoes, oats, yams, and blueberries, ideal for sustained energy.
Research Insight:
"Even when glycogen stores are depleted after 4.5 hours of activity at 70% VO2 max, athletes can still perform for an additional 2.5 hours at 66% VO2 max with proper fuel." – Coggan, Edward R., Medicine & Science in Sports & Exercise, 1998
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2. Don’t Overlook Electrolytes
Electrolytes help your body retain water, contract muscles, and maintain pH balance—critical during long races.
Symptoms of Electrolyte Imbalance Include:
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Muscle cramps
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Nausea
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Mental fog
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Decreased endurance
You can lose 2–6% of your body’s water weight just through sweat during a race, and much more during ultras. This loss leads to impaired performance and slower recovery.
Electrolyte Guidelines:
"Endurance athletes should consume 450–750mL of fluids per hour, including 300–600mg of sodium to maintain hydration and performance." – Kerksick, Chad M., Journal of the International Society of Sports Nutrition, 2017
Read the study
Pro Tip: Coconut water, pink Himalayan salt, and magnesium-rich supplements are excellent additions to your hydration strategy.
RELATED: 10 Symptoms Of Electrolyte Imbalance
3. Fuel With Essential Amino Acids (EAAs)
Your body doesn't just run on carbs—it also relies on essential amino acids to support muscle contraction, prevent central nervous system fatigue, and resist muscle breakdown.
What Happens During Catabolism:
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Muscle proteins break down to meet energy demands
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Tryptophan levels rise → increases serotonin → causes drowsiness
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Leads to central nervous system fatigue
"Ingesting EAAs during exercise supports muscle protein synthesis and delays both muscular and central fatigue." – Tipton, Kevin D., Current Opinion in Clinical Nutrition, 2009
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Suggested Supplement: Swolverine INTRA combines EAAs, B-vitamins, coconut water, tart cherry, and pomegranate for endurance, hydration, and recovery.
Other Key Nutritional Tips to Avoid Bonking
Add B-Vitamins
B-complex vitamins support neurotransmitter production, which helps reduce mental fatigue and keeps your nervous system firing during long events.
Test Your Fueling Strategy in Training
Never try a new gel, bar, or supplement on race day. Practice your fueling and hydration strategy during long training sessions to see how your body responds.
Symptoms of Bonking
Bonking doesn’t hit gradually—it slams into you. Recognizing the symptoms early can help you take action before it’s too late.
| Symptom | Description |
|---|---|
| Sudden Energy Crash | Legs feel heavy, and your pace slows dramatically despite effort. |
| Mental Fog | Trouble focusing, decision-making, or remembering race strategy. |
| Dizziness or Nausea | Lightheadedness, gastrointestinal discomfort, or queasiness. |
| Muscle Cramping | Linked to electrolyte imbalance and dehydration. |
| Loss of Coordination | Feeling unsteady or disoriented, increasing risk of tripping or stumbling. |
| Mood Swings or Apathy | Irritability, emotional lows, or a strong desire to quit mid-race. |
"The hallmark of glycogen depletion is central fatigue, causing mental and physical shutdown." – Jeukendrup, Sports Medicine
Read the study
Frequently Asked Questions About Bonking
Q: How long does it take to bonk during a race?
Typically, bonking occurs between 90 minutes and 3 hours of sustained endurance activity, especially if you're under-fueled or dehydrated.
Q: Can I recover from bonking mid-race?
Yes—but recovery is partial. Consuming fast-acting carbs, hydration, and electrolytes may allow you to finish, though not always at peak performance.
Q: Is bonking dangerous?
While not medically life-threatening, bonking impairs mental clarity, balance, and coordination, which increases the risk of injury—especially in hot or hilly environments.
Q: Can caffeine help prevent bonking?
Caffeine can delay fatigue by improving central nervous system output and enhancing fat oxidation, but it is not a replacement for carbs or amino acids.
Train Your Gut for Race Day
Your stomach is a muscle—and it can be trained too. Athletes often experience GI distress during races because they haven’t practiced fueling during training.
By gradually increasing carbohydrate intake during long workouts (e.g., 30g, then 45g, then 60g/hour), your gut can adapt to absorb and utilize more fuel without discomfort.
"Gut training improves gastric tolerance, enhances carb oxidation, and may reduce gastrointestinal symptoms during exercise." – Costa, R.J.S., Sports Medicine, 2017
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Pro Tip: Test your exact race-day fueling strategy—including gels, fluids, and supplements—in training runs at race pace to avoid surprises.
Bonk-Proof Race Day Checklist ✅
Use this checklist to optimize your endurance performance and reduce the risk of bonking:
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Carb Load: Eat 8–12g/kg of carbs daily for 24–48 hours before race day
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In-Race Fuel: Consume 30–60g of carbohydrates every hour
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Hydration Strategy: Drink 450–750mL of fluids per hour with 300–600mg sodium
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Electrolyte Support: Include magnesium, potassium, and sodium in your race-day mix
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EAA Supplementation: Take essential amino acids hourly to delay central fatigue
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Practice in Training: Test every product and strategy before race day
“Fueling isn't just a detail—it's the difference between finishing and failing.” – Burke, Louise M., Journal of Sports Sciences
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Takeaway: Fuel Smarter, Not Just Harder
Without a well-rounded performance nutrition protocol, your risk of hitting the wall increases dramatically.
Focus on:
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✅ Carbohydrate loading and intra-race fueling
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✅ Electrolyte and fluid replacement
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✅ Hourly EAA intake to reduce muscle fatigue
"Nutrition is not just a part of endurance performance—it is the cornerstone." – Jeukendrup, Asker E., Sports Medicine, 2014
Read the study
To perform at your best, plan your fueling, prep your supplements, and train with purpose. Avoid bonking by giving your body the energy, hydration, and nutrients it needs—mile after mile.
The Best Supplement To Avoid The Bonk, Is INTRA Workout Supplement From Swolverine
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 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.
