Why runners hit the wall, and how to avoid it
Hitting the wall is mostly a pacing failure, and it is costly: about 30 minutes for those who hit it. In a study of 4.1 million results it happened to 28% of men and 17% of women. Start conservatively, set a goal your recent training supports, and fuel from the start.
What to do
- Base your goal time on recent training and races, not on an online calculator or your watch's prediction. Simple formulas tend to be too optimistic.
- Run the first 5–10 km about 1–3% slower than goal pace. This is a coaching convention, not a tested number.
- If you are more than about 2% ahead of goal pace after 10 km, slow down.
- Push on only after about 30 km, and only if your effort still feels controlled.
- Eat from the start: about 60 g of carbohydrate per hour, practised in training.
- If you are a man chasing a personal best, be extra careful about the first half.
What “hitting the wall” means
Runners use the phrase loosely. Researchers need a definition. In the largest study of the wall, Smyth (2021) defined it as slowing by at least 20% for at least 5 km after the 25 km mark. That is the sudden late-race collapse many runners know, not just a slightly slower second half.
How common it is, and what it costs
Smyth analysed 4.1 million marathon results.
- 28% of men and 17% of women hit the wall by that definition.
- Those who hit it lost about 31.5 minutes (men) and 33.2 minutes (women).
Few training changes come close to half an hour. Avoiding the wall is one of the biggest gains on offer to recreational marathoners.
Why it happens
The pattern in the data points mostly at pacing. Women pace more evenly and hit the wall less. Among men, the rate of hitting the wall rose from 26% to 40% in the years just before a personal best. That is when runners push hardest and are most tempted to start too fast.
A second study puts numbers on what “too fast” means. Critical speed (CS) is roughly the fastest pace you can hold for a long time before fatigue builds rapidly. It can be estimated from your best efforts in normal training. In more than 25,000 runners, CS estimated this way predicted marathon time to within about 7.7% (Smyth and Muniz-Pumares, 2020). Two findings matter for race day:
- Recreational runners could hold only 79–93% of their CS for a full marathon, depending on ability.
- Running the first half above 94% of CS predicted large slowdowns later.
In plain terms, a pace that feels comfortable at 10 km can still be too fast for 42 km.
Fuelling plays a part too. The only marathon trial in recreational runners found that a planned fuelling strategy of about 60 g of carbohydrate an hour was about 11 minutes faster than eating freely. See how many carbs per hour in a marathon for the details.
Goal setting: calculators are too optimistic
Many runners pick a goal time from a calculator. The common Riegel formula, which projects a marathon time from a shorter race, predicted times that were at least 10 minutes too fast for half of recreational runners (Vickers and Vertosick, 2016). The same study found that weekly training volume added useful information beyond the shorter race time.
So treat a calculator result as the fastest plausible time, not a target. That is our suggestion, based on how often the formula overshoots.
A pacing plan
The research shows that going out too fast causes trouble. It doesn’t test a specific pacing plan. The plan below is a coaching convention built on those findings:
- Aim for even effort, not even splits, on a hilly course.
- Run the first 5–10 km 1–3% slower than goal pace. For a 4-hour goal (about 5:41 per km), that is roughly 5:45–5:52 per km.
- Check yourself at 10 km. If you are more than about 2% ahead of plan, ease off.
- Decide at 30 km. If your heart rate and effort have stayed under control, you can push. If not, hold pace.
Heat makes all of this harder. In elite marathoners, performance fell about 0.3–0.4% for each degree of heat stress above a cool optimum (Mantzios and colleagues, 2022). Our suggestion: on a warm day, start slower still.
What about men and women?
Women hit the wall less often in Smyth’s data and pace more evenly. Press coverage of a 2026 Berlin Marathon analysis reported that men were up to six times as likely to hit the wall among sub-3-hour finishers (Euronews, 2026). We have seen this only as a news report, not the study itself, so treat the number with caution.
The physiology doesn’t call for different pace rules by sex. The practical difference is where the risk sits: men chasing a personal best are the group most likely to go out too fast.
What we don’t know
- The big studies are observational. They show who hit the wall, not exactly why each runner did.
- The pacing plan’s numbers are convention. No trial has compared starting 1% slow against 3% slow.
- No predictor is exact. Even critical speed from training data missed marathon times by several percent on average.
- The heat figures come from elite runners. Whether slower runners lose more or less in heat is disputed.
- The Berlin figure is press coverage only.
Sources
- Smyth (2021). How recreational marathoners hit the wall: an analysis of 4.1 million race results.
- Smyth and Muniz-Pumares (2020). Critical speed from training data and marathon pacing in more than 25,000 runners.
- Vickers and Vertosick (2016). How well race-time formulas predict recreational marathon times.
- Hansen et al. (2014). Planned vs self-chosen fuelling in the Copenhagen Marathon.
- Mantzios et al. (2022). Heat stress and elite marathon performance.
- Euronews (2026). Press coverage of a Berlin Marathon analysis of the wall by sex.
Last reviewed 13 November 2026.