NutritionAnswer

HOW DO I AVOID BONKING WHILE CYCLING?

By Anthony WalshRoadman CyclingUpdated 10 July 2026

ANSWER

Bonking — the sudden, severe energy crash when muscle and liver glycogen are depleted — is prevented through three actions: eating 60-90g of carbohydrates per hour starting from the first 20 minutes of any ride over 90 minutes, carb-loading with 8-10g/kg of carbs in the 24 hours before a long event, and pacing conservatively to avoid burning through glycogen too quickly. Glycogen stores typically last 90-120 minutes at moderate intensity. Once depleted, power output drops by 30-50% and the sensation is unmistakable — sudden weakness, confusion, and inability to maintain even easy pedalling.

KEY TAKEAWAYS

Glycogen stores last 90-120 minutes at moderate intensity — after that, you are reliant on what you eat during the ride.
60-90g of carbohydrates per hour from mixed glucose-fructose sources prevents depletion during long rides.
Carb-loading (8-10g/kg in the 24 hours before) maximises starting glycogen and extends time to depletion by 20-30 minutes.
Pacing above threshold burns glycogen at an accelerated rate — staying below 75% FTP on long rides preserves stores significantly.

WHO THIS IS FOR

IS THIS YOU?

Riders who consistently hit the wall on rides over three hours

You feel strong for the first couple of hours then crash hard, losing power and motivation in the final quarter of the ride.

Sportive riders who want to finish strong rather than crawling home

You want a fuelling plan that ensures you have energy for the final hills rather than surviving on willpower alone.

THE ROADMAN VIEW

Bonking is entirely preventable. Every rider who has experienced it remembers it vividly — the sudden emptiness, the inability to push even 100 watts, the long, miserable crawl home. But it is not bad luck or poor fitness. It is a fuelling failure, and it has a precise, evidence-based solution.

The fix is boring but effective: eat early, eat often, eat enough. Most riders who bonk either started eating too late, ate too little, or went too hard in the first half and burned through glycogen at an unsustainable rate. A disciplined fuelling plan and sensible pacing will prevent it every single time.

EXPERT EVIDENCE

WHAT THE EXPERTS SAY

Prof Asker JeukendrupSports nutrition researcher, Mysportscience
Bonking is a glycogen depletion event. The liver's role is to maintain blood glucose for brain function, while muscle glycogen fuels contraction. When both sources are exhausted, the brain reduces motor drive to protect itself. The performance decline is not a choice — it is a physiological safety mechanism. Prevention through exogenous carbohydrate intake is straightforward: match intake to expenditure rate, using dual-source carbohydrates to maximise absorption.

PRACTICAL APPLICATION

DO THIS WEEK

Start eating from the first 20 minutes of any long ride
Do not wait until you feel hungry. Set a repeating 20-minute timer on your head unit and eat something at every alarm — a gel, a section of energy bar, or a few sips of carbohydrate drink. By the time hunger signals arrive, glycogen is already significantly depleted. Eating early is insurance against the crash.
Carb-load properly in the 24 hours before a long event
Eat 8-10g of carbohydrate per kilogram of body weight the day before a sportive or long ride. For a 75kg rider, that is 600-750g of carbs — roughly equivalent to 10-12 large servings of pasta, rice, or bread spread across all meals and snacks. This maximises muscle glycogen stores and delays depletion by 20-30 minutes compared to a normal diet.
Pace the first half conservatively
Keep intensity below 75% of FTP for the first half of any ride over three hours. Higher intensities shift the fuel mix towards glycogen and away from fat oxidation. Riding at 65-70% FTP for the first two hours preserves glycogen for when the route gets harder or fatigue sets in later. The riders who finish strongest are usually the ones who started most conservatively.

COMMON MISTAKES

WHAT CYCLISTS GET WRONG

MISTAKERelying on fat adaptation to avoid bonking on long rides.
FIXEven well-adapted endurance athletes cannot sustain moderate-to-high intensities on fat alone. Fat oxidation supports easy riding but cannot match glycogen's contribution at intensities above ~65% FTP. Eat carbohydrates regardless of your metabolic flexibility.
MISTAKEEating a large meal right before the ride instead of carb-loading the day before.
FIXA big pre-ride meal cannot compensate for low glycogen stores. Glycogen synthesis takes 24+ hours. A massive breakfast might cause stomach problems on the bike. Carb-load the day before, eat a moderate breakfast 2-3 hours before the ride, and fuel consistently during the ride.
MISTAKEGoing too hard on the first climb and depleting glycogen early.
FIXThe effort that feels sustainable at minute 30 can be catastrophic by hour 3 if it is burning glycogen faster than you can replace it. Monitor power on early climbs and resist the urge to go deep. Save the matches for the final third of the ride.

FAQ

FREQUENTLY ASKED QUESTIONS

How do I know if I am about to bonk?

Early warning signs include sudden loss of power, difficulty maintaining cadence, lightheadedness, irritability, and an inability to concentrate. Some riders describe a 'hollow' sensation in the legs. If you notice these signs, immediately consume fast-acting carbohydrate (a gel or sugary drink) and reduce intensity significantly. Catching it early allows partial recovery within 10-15 minutes.

Can you recover from a bonk mid-ride?

Partially. Consuming 40-60g of fast-acting carbohydrate and reducing intensity to very easy riding for 15-20 minutes can restore enough blood glucose for brain function and allow you to continue at a reduced pace. However, depleted muscle glycogen does not fully replenish during exercise — you will not return to your previous performance level. The rest of the ride will be significantly slower.

Do fitter riders bonk less often?

Fitter riders have higher fat oxidation rates at a given percentage of their maximum, which spares glycogen. They also tend to have better fuelling habits. But a fit rider who does not eat enough on a long ride will bonk just as hard as anyone else — fitness does not replace fuel. The fitter you are, the harder you can ride, and the more carbohydrate you need to sustain that output.