Glossary: Bonk (hitting the wall)

What a bonk is

The "bonk" (cycling term) or "hitting the wall" (marathon term) is severe carbohydrate depletion during long exercise. Liver and muscle glycogen drop low enough that the body can no longer sustain pace.

Symptoms (in rough order of onset):

• Sudden loss of pace despite normal effort.
• HR climbs at the same pace.
• Mental fog, irritability, poor decision-making.
• Shaky, weak legs.
• Cold sweat, sometimes nausea.
• In severe cases, near-loss of consciousness.

When it happens

• Long efforts: typically after 90+ minutes of moderate to hard exercise.
• Pre-race under-fueling: starting with low glycogen reserves accelerates the problem.
• In-race under-fueling: not consuming enough CHO per hour during the race.
• Pre-race carb loading missed or insufficient.
• High intensity: pushing above sweet spot for sustained periods depletes glycogen faster.

How to avoid it

Before race day

• Follow the carb loading protocol for races over 90 minutes.
• Practice race-day fueling in training. Find products that your stomach tolerates at race pace.

Race morning

• Eat the standard pre-race meal (see Race morning routine).
• Top up with a snack 60 to 90 minutes before the start.

In the race

• Follow your fueling plan.
• 60 to 90 g of carbs per hour for most athletes on long course bike and run.
• Drink at every aid station even if not thirsty.
• Do not skip fueling because you "feel fine"; the moment you feel hungry mid-race, you are already behind.

After race day

• Refuel within 60 minutes (carbs + protein).

What to do if it starts

The moment you notice early symptoms:

• Slow down immediately. Walking on the run is fine. Soft pedaling on the bike is fine. Continuing at race pace makes it worse fast.
• Eat fast carbs. Gel, gummies, sports drink, even cola. Whatever is on hand.
• Hydrate with electrolyte mix.
• Wait 10 to 20 minutes for the glucose to take effect. You can usually resume at reduced pace.

What the Hub does

The fueling planner builds an hour-by-hour CHO schedule to keep you ahead of glycogen depletion. Follow the schedule even when you feel fine.

See also: Race carb-loading protocol, Fueling planner, Race morning routine.