You’re two hours into a Saturday ride when your legs turn to concrete and your brain goes foggy. You can barely turn the pedals. That’s what bonking is, and it happens to nearly every cyclist….. eventually.
The good news?
It’s completely preventable once you understand why it happens and how to fuel around it.
No special gear required, just a plan.
What Exactly Is Bonking?
Most cyclists have confused bonking with just being tired. They’re not the same thing, and knowing the difference matters.
Bonking is the near-total depletion of glycogen, your muscles’ primary fuel source during cycling. Runners call it “hitting the wall.” Your body stores roughly 1,600 to 3,600 calories of glycogen across your muscles and liver. That sounds like a lot, but at a moderate recreational pace (60-70% of max heart rate), you’ll burn through those stores in about two to three hours. Push harder and that window shrinks to 90 minutes.
💡 The difference between bonking and normal tiredness is stark. Regular fatigue builds gradually. Your legs burn, your heart rate climbs, but your head stays clear. Bonking hits like a switch.
Your brain runs on glucose. When blood sugar drops, your brain slams the brakes on muscle output to protect itself. Scientists call this the central governor theory.
Your brain creates overwhelming fatigue, not because your legs can’t physically move, but because it’s rationing the last drops of fuel for its own survival.
That’s why bonking comes with confusion, dizziness, and nausea, not just heavy legs. It’s a whole-body shutdown, not a muscle problem.
Warning Signs You’re About to Bonk
The best time to deal with a bonk is before it fully arrives.
Early warning signs (you can still save the ride): unusual hunger, slight lightheadedness, legs feeling heavier than the effort warrants, difficulty holding a conversation, and sudden irritability. If your riding buddy asks why you’re snapping at them, reach for a gel.
Full bonk symptoms (you’re already in trouble): extreme weakness, nausea, shaking hands, blurred vision, mental fog, and a feeling of dread. Riders who’ve experienced it describe going from fine to dreadful in seconds, with confusion, dizziness, and a sudden urge to question every life choice that led to this ride.
Try this if you’re unsure: eat something sugary and wait 15-20 minutes. If you feel dramatically better, that was a bonk. Normal fatigue won’t respond the same way to a quick sugar hit.
Why Bonking Happens: Your Glycogen Budget
Every ride runs on a fuel budget, and most recreational cyclists have no idea how small it is. Your body stores around 2,000 usable calories of glycogen. At a typical recreational pace, that gives you a two-to-three-hour window before the tank runs dry.
Fat can’t save you here. Your body has tens of thousands of fat calories available, but fat requires more oxygen to burn and can’t deliver energy fast enough to sustain cycling intensity. When glycogen runs out, your pace drops dramatically.
🍳 Skipping breakfast before a Saturday morning ride makes this worse. You’ve started with a half-empty tank, and your safe window before bonking just got cut significantly.
Bonking also carries consequences beyond the ride itself. Glycogen depletion triggers muscle protein breakdown and suppresses your immune system, meaning you recover slower and get sick easier in the days after.
Lab testing revealed another surprise: body size doesn’t strongly predict glycogen needs. Researchers found similar glucose oxidation rates (44g versus 46g per hour) in athletes of dramatically different sizes. Your depletion timeline depends more on intensity and duration than body size.
How to Prevent Bonking on Every Ride
Prevention comes down to keeping fuel going in while fuel is going out. You know the burn rate. Match it.
Before the ride (2-3 hours out): Eat a carb-rich meal. Oatmeal with banana, toast with peanut butter, or pasta. Aim for roughly 1-2g of carbs per kilogram of bodyweight. For a 155-pound rider, that’s about 70-140g of carbs.
The golden rule for during the ride: Start eating at 20-30 minutes in, NOT when you feel hungry. By the time hunger hits, your tank is already running on fumes.
How much: For rides over 90 minutes, aim for 30-60g of carbs per hour. That’s roughly one energy gel or a banana every 30 minutes. For rides over two hours, push toward 60-90g per hour.
What to eat: Energy gels work fastest (about 5 minutes to hit your system). Sports drink mixes combine hydration with fuel. Energy bars take 15-20 minutes but feel more satisfying. Real food like dates, bananas and rice cakes with jam work great too.
Sip, don’t gulp. Small amounts every 15-20 minutes beats one big feed every hour. Your gut handles a steady trickle far better than sudden loads. Keep water flowing too: 150-250ml every 15-20 minutes with water or an electrolyte drink.
If eating during rides gives you stomach trouble, start small at 30g per hour and gradually increase over several weeks. Your gut adapts just like your legs do.
What to Do If You Bonk Mid-Ride
Prevention doesn’t always work perfectly. Maybe you forgot your gels, underestimated the ride, or just got caught out. Follow this emergency protocol.
Stop or slow way down. Don’t try to push through. Your brain is actively restricting muscle output to protect itself, and fighting it risks a crash.
Eat fast-acting sugar. Energy gel with water, jelly beans, a jam sandwich, or even a can of full-sugar cola from a gas station. You need simple sugars right now, not a granola bar.
Wait 15-20 minutes. That’s how long it takes for carbs to reach your bloodstream. Resist the urge to eat four gels in a panic. That’ll just upset your stomach.
Ride home easy. Once you feel better, keep the pace gentle and continue eating every 20 minutes. Save the hard efforts for next time.
Some lingering fatigue after a bonk is normal and can last a day or two. Eat a proper meal with carbs and protein within 30 minutes of getting home.
Every bonk is a learning moment. Note what you ate (or didn’t), when you ate it, and how long the ride was. Adjust your fueling plan for next time. After one or two lessons, most riders never bonk again.
I hope this article has been useful to you. Please feel free to leave a comment or share 👇
