What Happens When You Bonk on the Bike

Bonking – hitting the wall – represents complete glycogen depletion with devastating effects on performance and wellbeing. Understanding the physiological cascade helps you prevent this miserable experience and recognize early warning signs.

The Physiology of Bonking

Your muscles and liver store approximately 2000 calories of glycogen – enough for 90 minutes of moderate cycling. Once these stores deplete, your body shifts to fat metabolism which produces energy far slower than carbohydrate burning.

At threshold efforts, you burn primarily glycogen. Drain those reserves and power output crashes 30-50% almost instantly. Your legs feel empty and hollow. Even spinning easy gears at 12mph feels impossible.

Brain Function Deteriorates

Your brain relies exclusively on glucose for fuel. As blood sugar drops, cognitive function degrades rapidly. Decision-making suffers, reaction time slows, and emotions become erratic. Irritability, confusion, and even irrational behavior emerge.

Cyclists report feeling detached from reality during severe bonks. Simple navigation becomes challenging. Some riders forget where they’re going or why they’re riding. This mental impairment creates safety risks in traffic.

Physical Symptoms Progress

Early signs include subtle fatigue and slightly reduced power. Legs feel heavy and cadence drops. You might feel hungry or crave sweets intensely. Ignore these warnings and symptoms escalate.

Moderate bonking brings profound weakness, inability to maintain pace, and desperate hunger. Dizziness and lightheadedness develop. Sweating may decrease as your body conserves resources.

Severe bonking causes complete inability to pedal effectively, vision problems, and emotional breakdown. Some riders cry or become angry. Nausea prevents eating even though food is desperately needed. You must stop riding.

The Recovery Process

Consuming carbohydrates reverses bonking but recovery takes 30-60 minutes. Simple sugars work fastest – soda, gel, or candy provide quick glucose. Your stomach may rebel against food initially, requiring small, frequent bites.

Find shade and rest while consuming 60-100g carbs. Your body needs time to digest and convert food to usable energy. Trying to ride through a severe bonk only worsens the situation.

Full recovery to normal performance requires several hours and complete glycogen replenishment through substantial meals. The remainder of that day’s ride will feel harder than usual.

Long-Term Effects

Repeated bonking damages your metabolism and can suppress immune function for days. Athletes who regularly deplete glycogen stores completely may develop chronic fatigue and overtraining symptoms.

One severe bonk won’t cause lasting problems if you recover properly. Make it a habit and you risk hormonal disruption, illness, and burnout.

Prevention Strategies

Consume 60-90g carbs per hour for rides exceeding 90 minutes. Start fueling early – waiting until you feel depleted means you’re already behind. Carry more nutrition than you think you need.

Pace appropriately for your fitness. Riding too hard burns glycogen faster than you can replace it. Even perfect nutrition can’t prevent bonking if intensity exceeds your aerobic capacity for hours.

Practice nutrition during training rides. Don’t experiment on event day. Your gut adapts to processing food while exercising through consistent training.