Bonking
Bonking / Hitting the Wall
Bonking (hitting the wall) occurs when glycogen stores deplete during exercise, causing sudden fatigue and performance collapse. Learn how to prevent and recover from bonking.
Quick Answer
Bonking — (hitting the wall) is the sudden onset of fatigue and weakness that occurs when glycogen stores are depleted during prolonged exercise. It typically happens 90-120 minutes into intense exercise when the body can no longer maintain blood glucose levels for muscle and brain function.
What is Bonking?
Bonking occurs when your body runs out of readily available carbohydrate fuel:
| What Happens | Result |
|---|---|
| Glycogen depletes | No muscle fuel |
| Blood sugar drops | Brain dysfunction |
| Fat burning can't keep up | Forced to slow dramatically |
The result: Sudden, severe fatigue that makes continuing at pace impossible.
Bonking Symptoms
Physical Symptoms
| Symptom | Description |
|---|---|
| Severe leg weakness | Legs feel like lead |
| Muscle trembling | Shakiness |
| Profound fatigue | Can barely move |
| Cold sweats | Despite exertion |
| Nausea | Stomach upset |
| Coordination loss | Wobbly movements |
Mental Symptoms
| Symptom | Description |
|---|---|
| Confusion | Difficulty thinking |
| Irritability | Mood changes |
| Depression | Hopelessness |
| Tunnel vision | Narrowed focus |
| Poor decision-making | Judgment impaired |
| Desire to quit | Overwhelming |
Read more: How to Avoid Hitting the Wall.
Why Bonking Happens
The Physiology
- Glycogen depletes: Muscles run out of stored carbs
- Blood sugar drops: Liver can't maintain glucose levels
- Brain starves: Brain requires glucose to function
- Fat burning insufficient: Can't provide energy fast enough
- Performance collapses: Body protects vital functions
Typical Timeline
| Exercise Duration | Glycogen Status |
|---|---|
| 0-60 min | Adequate |
| 60-90 min | Declining |
| 90-120 min | Critical |
| 120+ min without fueling | Depleted (bonk risk) |
Bonking vs Dehydration
| Factor | Bonking | Dehydration |
|---|---|---|
| Cause | Low glycogen | Low fluids |
| Onset | Often sudden | Usually gradual |
| Main symptom | Profound weakness | Thirst, headache |
| Mental effects | Confusion, irritability | Fatigue, dizziness |
| Recovery | Eat carbs, 15-30 min | Drink fluids, longer |
Learn to differentiate: Cycling Bonking vs Dehydration.
Preventing Bonking
Before Exercise
| Strategy | Details |
|---|---|
| Carb load | 2-3 days before long events |
| Pre-exercise meal | 2-3g carbs/kg, 3-4 hours before |
| Top off glycogen | Small carb snack 1 hour before |
During Exercise
| Duration | Fueling Strategy |
|---|---|
| < 60 min | Usually nothing needed |
| 60-90 min | 30-40g carbs/hour |
| 90+ min | 60-90g carbs/hour |
| Ultra events | Up to 100g carbs/hour (trained) |
Key: Start fueling early, before you feel hungry.
Fueling Options
| Source | Carbs | Notes |
|---|---|---|
| Sports drink (500ml) | 30-35g | Also provides fluid |
| Energy gel | 20-25g | Easy to carry |
| Banana | 25-30g | Solid food option |
| Energy bar | 25-45g | Requires chewing |
| Dates (3-4) | 20-25g | Natural option |
Read: How to Fuel During Long Rides.
Recovering from a Bonk
Immediate Actions
| Step | Action |
|---|---|
| 1 | Stop or slow dramatically |
| 2 | Consume simple carbs immediately |
| 3 | Wait 15-30 minutes |
| 4 | Assess before continuing |
Best Foods When Bonking
| Food | Why It Works |
|---|---|
| Soda/Coke | Fast sugar, caffeine |
| Energy gel with water | Quick absorption |
| Sports drink | Sugar + hydration |
| Candy | Pure sugar |
| Honey | Fast absorbing |
Recovery Timeline
| Time After Carbs | Expected Recovery |
|---|---|
| 5-10 min | Begin feeling better |
| 15-20 min | Mental clarity returns |
| 20-30 min | Can resume (at reduced intensity) |
| Full recovery | May not happen during event |
Training to Prevent Bonking
Metabolic Efficiency
Train your body to use fat more efficiently:
| Strategy | How It Helps |
|---|---|
| Zone 2 training | Improves fat oxidation |
| Fasted training | Teaches fat adaptation |
| Long, easy efforts | Builds fuel efficiency |
| Practice race nutrition | Trains gut absorption |
Gut Training
Your gut must be trained to absorb carbs during exercise:
| Week | Carb Intake During Training |
|---|---|
| 1-2 | 30g/hour |
| 3-4 | 45g/hour |
| 5-6 | 60g/hour |
| 7-8 | 75-90g/hour |
Common Bonking Mistakes
1. Starting Too Fast
Going out too fast depletes glycogen faster:
- Solution: Pace conservatively, especially early
2. Forgetting to Eat
Easy to forget during racing:
- Solution: Set timer reminders every 20-30 minutes
3. New Race Nutrition
GI issues prevent absorption:
- Solution: Practice race nutrition in training
4. All-or-Nothing Eating
Either nothing or too much:
- Solution: Small, frequent intake
Common Questions
Can you un-bonk during a race?
Partially. You can recover enough to continue, but rarely at original intensity. Prevention is far better than cure.
Does bonking cause permanent damage?
No—bonking is temporary, though deeply unpleasant. Full recovery happens within hours with proper nutrition.
Why do some people bonk earlier than others?
Factors include:
- Starting glycogen levels
- Pacing (faster = faster depletion)
- Training (better trained = better fat use)
- Fueling during event
- Individual metabolism
Can fat-adapted athletes avoid bonking?
Better fat adaptation helps delay bonking, but high-intensity efforts still require glycogen. No one is immune if glycogen depletes completely.