You hit mile 18 of the marathon, the legs go to lead, the world narrows, and finishing seems impossible. That is the bonk. The good news: a structured 30-minute response can put you back in the race — not at goal pace, but moving forward and finishing intact. Here is the protocol.
The one-sentence answer
Slow to a walk, dose 30–60 g of fast carbs, take 500 mg of sodium with water, walk 5–10 minutes while the fuel lands, then resume at a pace you can hold to the finish.
Diagnose which bonk you are in
Three failures look identical from the inside but require different fixes:
- Glycogen depletion (true bonk). Symptoms come on fast — heavy legs, mental fog, sudden pace drop, occasionally tunnel vision. Fix: fast carbs.
- Sodium loss. Cramping (especially calves and quads), nausea, puffy fingers. Fix: salt + water, not more sugar. See our hyponatremia prevention guide.
- GI shutdown. Bloating, sloshing, nausea without hunger. Fix: stop ingesting carbs, sip plain water with sodium only, walk it out.
Most race-day bonks are glycogen-driven. If you are unsure, default to glycogen first.
The 30-minute protocol — minute by minute
0–2 min: Walk. Stop the bleed. Take one gel + several sips of water.
2–5 min: Take a salt tablet or salt-heavy chew (≈500 mg sodium). Sip water. Keep walking.
5–15 min: Continue walking. Take a second gel at minute 10 if the first one has not lifted you. Sip cola if available — sugar lands faster than gels in the desperate case.
15–25 min: Begin a light jog. Hold an effort 30 sec per mile slower than your bonk pace. Reassess at 25 minutes.
25–30 min: If symptoms cleared, settle at a sustainable pace and finish. If not, walk-jog the rest.
When sugar will not land
If the gut has shut down, gels will sit in the stomach and make everything worse. Switch to:
- Cola from aid stations (carbonation helps — open and let some fizz out)
- Salted broth or soup
- Plain water with a salt tab — defer carbs until the gut comes back
- Ginger candy or chew — slows nausea
Caffeine in a rescue
A caffeinated gel can lift perceived effort enough to mask the worst of the bonk while real carbs absorb. Use one caffeinated gel as part of the 5–15 minute window if you are not already saturated. Do not stack four caffeinated gels — see dosing limits in our caffeine strategy guide.
How to avoid the next one
Four rules — each linked to a deeper protocol:
- Fuel earlier and more consistently — see marathon gel count and timing
- Train the gut to absorb at race-day rates — see gut training for endurance
- Carb-load properly — see 3-day carb loading
- Pace below threshold for the first 30 km — see how to avoid hitting the wall
When to DNF
Some bonks should not be ridden out. Stop at the next medical tent if you experience:
- Vomiting that does not pass
- Confusion, slurred speech, disorientation
- Stopped sweating in hot conditions
- Cannot walk in a straight line
- Chest pain or arrhythmia
A bonk is recoverable. Heat stroke and severe hyponatremia kill — trade a finish for a hospital stay only if you have to.
Frequently asked questions
How long after a bonk can I keep racing? 20–30 minutes of correct response usually restores 70–80% of baseline effort. Goal pace is gone; finish is recoverable.
Can caffeine alone fix a bonk? No. Caffeine masks effort; sugar fixes the cause. Use them together.
Is it safe to push through? Pushing through glycogen depletion is mostly safe but very slow. Pushing through severe sodium loss is dangerous. Diagnose first.
Sugar high crash from too many gels? Very rare in running — the high glucose oxidation rate of moderate-to-hard running prevents the reactive hypoglycemia you might see at rest.