Male marathon runners hit the wall more often mainly because they burn through carbohydrate stores faster than women and tend to start races too aggressively. "Bonking," or hitting the wall, is the sudden crash that comes when your muscles and liver run out of glycogen—their stored carbohydrate fuel—usually around mile 20. Prevention comes down to two levers you control: how you fuel and how you pace. This article explains why the sex gap exists, what the evidence actually shows, and the specific training and race-day steps that keep you moving when the wall would otherwise hit.
Medical information disclaimer: This article is for general educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a physician or other qualified health professional about symptoms, medications, tests, or treatment decisions.
Table of Contents
- What "the wall" actually is
- Why men hit the wall more than women
- It isn't only about fuel
- Race-day fueling to prevent the crash
- Training solutions that raise your ceiling
- Frequently Asked Questions
What "the wall" actually is
Bonking is glycogen depletion, not simple tiredness. Trained runners store roughly 400–500 grams of glycogen in their muscles plus another 90–120 grams in the liver, which covers only about 90 minutes of hard effort, according to Runners Connect's breakdown of marathon glycogen depletion. Once those tanks run low, your pace collapses and even easy running feels impossible—typically after mile 20.
The math is the problem. A marathon takes most runners three to five hours, but your stored fuel lasts about an hour and a half at race intensity. Without replacing carbohydrate along the way, or teaching your body to lean more on fat, you will run out before the finish line.
Why men hit the wall more than women
The pattern is well documented across large data sets. In an analysis of about 92,000 U.S. runners across 14 marathons, men slowed by roughly 15.6% in the second half versus 11.7% for women, and men were about three times more likely to slow by 30% or more, reported Deaner and colleagues in Medicine & Science in Sports & Exercise.
A separate study of roughly 873,000 Berlin Marathon finishers found men about twice as likely to hit the wall as women, per research published in Scientific Reports. Part of the gap is metabolic. Women oxidize more fat and less carbohydrate during endurance exercise and show evidence of sparing muscle glycogen, an effect linked partly to the hormone 17-β-estradiol shifting fuel use toward free fatty acids, according to Devries's work in Medicine & Science in Sports & Exercise. Burning proportionally less glycogen means women reach the wall later.
It isn't only about fuel
Metabolism explains part of the difference, but behavior matters too. Researchers attribute men's greater slowing partly to riskier early pacing and decision-making, and possibly greater susceptibility to overheating—factors that have nothing to do with glycogen chemistry, as noted in the same Deaner study. In plain terms, more men go out too fast and pay for it late.
The sex gap also isn't absolute. A newer analysis argues the "women simply pace smarter" story gets more complicated once you account for fitness and experience, as covered by Outside. The practical takeaway holds regardless: aggressive early pacing and poor fueling raise anyone's risk, and those are exactly the things you can change.
Race-day fueling to prevent the crash
For any effort longer than 90 minutes, you need to take in carbohydrate while you run. Aim for about 30–60 grams per hour, starting early—within the first 20–45 minutes—in small doses every 15–20 minutes rather than one large hit, advises Runners Connect's guide to avoiding the wall. Starting before you feel low matters, because you can't refill an empty tank mid-race.
There is a ceiling on how fast your gut absorbs sugar. Single-source glucose tops out near 1 gram per minute, about 60 grams per hour, but a 2:1 glucose–fructose mix uses a second absorption pathway to reach roughly 1.5 grams per minute, or 90 grams per hour, explains the Cadence carbohydrate fuel guide. That physiology is why higher-end fueling requires mixed-sugar gels or drinks, not just more of one type. A simple race-fueling checklist:.
- Practice your exact gels or drinks in long training runs—never test new products on race day.
- Take your first carbohydrate within 20–45 minutes, not at mile 18.
- Spread intake into small amounts every 15–20 minutes.
- Use glucose–fructose products if you're targeting more than 60 grams per hour.
- Pair carbohydrate with water to aid absorption.
Training solutions that raise your ceiling
Fueling handles race day; training changes what your body can store and how sensibly you run. Carbohydrate loading—elevating your carb intake in the days before the race—tops off glycogen stores, while conservative even or negative-split pacing addresses the decision-making side of the wall, according to Runners Connect. Together they target both the metabolic and behavioral drivers at once.
Negative splitting means running the second half as fast or faster than the first. It directly counters the aggressive early pacing that pushes more men into a late-race collapse. Rehearse it: run your long training runs with a controlled first half so the discipline feels automatic when adrenaline pushes you to sprint the opening miles. For a deeper look at the pacing research, the full study by Deaner and colleagues, "Men Are More Likely than Women to Slow in the Marathon," lays out the data behind these patterns.
Frequently Asked Questions
How many grams of carbs per hour do I really need in a marathon?
Aim for 30–60 grams per hour, and up to about 90 grams with a glucose–fructose mix if your gut tolerates it after practice.
Does carbohydrate loading eliminate the risk of bonking?
No. Loading tops off your glycogen, but stored fuel still lasts only about 90 minutes at race pace, so you must also fuel during the race.
Why do I hit the wall around mile 20 specifically?
That's roughly where most runners exhaust their stored glycogen, since those tanks cover only about 90 minutes of hard effort.
