Why you crash on a long hike (and how to stop it)
That heavy, flat, grumpy feeling a few hours in is not weakness. It is usually fuel, fluid or pace, and all three are fixable.
- 4Causes
- 4 stepsTo fix it
- 6 minRead
Lauren Jones, Peaksted co-founder · Training advice reviewed by Nathan Gee · Updated 14 October 2026Almost everyone crashes on a long walk at some point, and almost everyone blames their fitness. It is usually not that. It is the snack you skipped two hours ago.
A crash usually means you are short on fuel, short on fluid, or both, often made worse by starting too fast. Fix it with a few quick carbs, a few sips and an easier pace, then prevent it with a small snack every hour.
Picture this hike
Same day, same person, one small change at 11:00.
- You set off feeling brilliant
Fresh legs, good weather, a spring in your step. You feel like you could do this all day. That feeling is the trap.
- You skip the snack
You are making good time and do not want to stop. You are not hungry, so you keep going. Your tank is quietly running down and you cannot feel it yet.
- Lunch is a rush
Now you are properly hungry. You eat fast and a lot, then feel heavy and sleepy on the next climb.
- Then it hits
Your legs go. Everything is effort. You snap at your friend about nothing. You have not suddenly got unfit. You ran low an hour ago and only just noticed.
Four ways to hit the wall
It is rarely one thing. Pick the one that sounds like you, then flip the card for the fix.
You ran out of easy fuel
It is mid-afternoon. Your legs have stopped taking orders and everything is suddenly a lot of effort. You are oddly grumpy and all you can think about is food.
- Heavy, flat legs
- Short temper
- Sudden hunger or sugar cravings
- Slow, clumsy steps
What is going on: Your muscles and liver hold a limited store of carbohydrate. You were using it faster than you were topping it up, and now the tank is low. It builds slowly and then hits all at once.
You are low on fluid
You have a dull headache and a foggy head. You realise you have not needed the toilet for hours and your mouth feels tacky.
- Dull headache
- Dark urine, or none
- Dry mouth
- Foggy and flat
What is going on: Even mild dehydration makes effort feel harder and thinking slower. It sneaks up in cool weather when you do not feel thirsty, and at altitude where you breathe out more water.
You spent it all early
You flew up the first climb feeling great and overtaking everyone. Three hours later you are crawling and wondering what happened.
- Strong start, then fading
- Breathing hard on gentle slopes
- Legs burning early
- Needing long breaks
What is going on: Hard effort burns carbohydrate much faster. An easy pace stretches your fuel across the whole day, so pacing is a fuelling skill as much as a fitness one.
You were behind from the start
You skipped breakfast because you were not hungry, snacked a bit, and then it was 2 pm and you felt awful. Nothing in your pack looks appealing.
- Not hungry, even when you need it
- Light-headed on climbs
- Food feels hard to face
- Struggling to catch up
What is going on: Heat, cold, nerves and altitude can all switch your appetite off just when you need food most. Once you are behind, it is hard to catch up in the middle of a day.
What to do in the moment
Warning signs: legs suddenly heavy, irritable, foggy or light-headed, craving sugar, clumsy on descents.
- Slow down
Take the pace right back. Walk, do not push.
- Eat quick carbs
A gel, a banana, jelly sweets or dried fruit. Around 20 to 30 g of carbohydrate.
- Sip some fluid
A few good sips. Add a little salt in the next meal or drink if it has been a long, sweaty day.
- Give it 10 to 15 minutes
Most people feel noticeably better, then keep eating little and often.
If someone is confused, vomiting, unable to walk straight or getting worse, treat it as more than a crash. Stop, get warm and dry, and get help. Cold, altitude illness and over-drinking can look similar.
How to stop it happening again
Three habits do most of the work.
- Eat something small every hour
Never more than two hours without food, and start in the first hour.
- Sip all day
A few mouthfuls every 10 to 15 minutes, not a big drink when you are thirsty.
- Start easy
If you can chat in sentences, you are about right. Our pacing guide, reviewed by Nathan, goes further.
Hiking crash: FAQ
What is bonking when hiking?
Bonking is another word for hitting the wall: a sudden drop in energy when your easy fuel runs low. Legs feel heavy, your head goes foggy and you may get shaky or grumpy. It is fixable with quick carbohydrate, a few sips of fluid and an easier pace.
How long does it take to recover from a hiking crash?
Many people feel noticeably better within 10 to 20 minutes of eating quick carbohydrate and slowing down. If you were also dehydrated or well behind on food, it can take a proper meal and a rest to feel normal again.
Why do I feel so tired halfway through a hike?
Most often it is fuel, fluid or pace. You may have eaten too little too late, drunk too little, or started too fast. Eating small amounts early and often, drinking steadily and keeping an easy pace fixes most of it.
Why do I get shaky or grumpy on a hike?
Both are common signs that your brain is short of easy fuel. When blood sugar dips, you can feel jittery, irritable and unable to think straight. A quick carbohydrate snack and a few minutes sitting down usually settles it.
Can poor sleep make a crash more likely?
It can. Tired people tend to eat less, pace less well and feel the effort as harder. It is one more reason to eat on a schedule rather than waiting for hunger on a day you slept badly.
Does altitude make it worse?
It can. Appetite often drops at altitude and you lose more water breathing, so crashes are easier to fall into. The altitude part of this series covers it.
The stronger your aerobic base, the longer you stay in easy-fuel territory. The free readiness check shows whether endurance is your gap, and Trek Ready builds it over eight weeks.
Check my readinessSources and scope
This is general sports-nutrition information, not personal dietary or medical advice. Carbohydrate guidance follows the joint position statement Nutrition and Athletic Performance (Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine, Journal of the Academy of Nutrition and Dietetics, 2016), adapted for hiking pace. Fluid guidance follows the American College of Sports Medicine position stand Exercise and Fluid Replacement (2007), which stresses that needs vary widely between people. The fuel-tank chart is an illustration of the pattern, not measured data. Further reading: Jeukendrup, A step towards personalized sports nutrition: carbohydrate intake during exercise (Sports Medicine, 2014), on carbohydrate intake and endurance performance. Lauren Jones is studying towards the NASM Sports Nutrition qualification. If you have a health condition, an allergy, diabetes or an eating concern, see a doctor or registered dietitian before changing how you eat. Training advice reviewed by Nathan Gee, BSc Sports Science.
