Bonk : Complete glycogen depletion (hunger knock)

Sudden performance collapse when muscle glycogen stores are exhausted : the dreaded 'wall' of long-distance racing.

The bonk (or 'hunger knock') occurs when muscle and liver glycogen stores are exhausted. The brain, dependent on glucose, sends distress signals: dizziness, confusion, leaden legs, urge to stop. The primary cause is insufficient carbohydrate intake during effort (especially in racing). Full recovery takes 15-30 min after ingesting fast-acting carbs. In Ironman, targeting 60-90 g of carbs per hour from the bike leg (maintained through the run) prevents complete depletion. Poor pacing at the start (too fast = accelerated glycogen combustion) is the number-one cause.