Racing smarter
Is a sub-4 marathon realistic? A five-input reality check
Sub-4 means holding 5:41/km (9:09/mi) for 42.195 km (26.2 mi). Five inputs decide it: a recent half under about 1:52, roughly 45 km (28 mi) a week, a longest run past 30 km (18.6 mi), the course, and the weather. Miss two and it is next year.
| What | Number | The qualifier |
|---|---|---|
| Pace required | 5:41/km (9:09/mi) | even, the whole way |
| Half-marathon marker | about 1:52 or faster | within the last 6 weeks |
| Weekly volume | 45 km (28 mi) or more | sustained for 8+ weeks |
| Longest run | past 30 km (18.6 mi) | at least twice |
| Heat cost | up to 4% slower | El Helou 2012; more for slower runners |
| Halfway target | 2:00:00, or 2:01:12 | even, or a 2% negative split |
What does sub-4 actually ask of you?
5:41 per kilometre, or 9:09 per mile, held for 42.195 km (26.2 mi).
That is the whole requirement, and it is worth looking at plainly. It is not a fast pace. Most people reading this can already run a kilometre at 5:41. The question is never the pace. It is the forty-second kilometre at that pace.
Halfway on even splits is 2:00:00. On a modest 2% negative split you would come through in 2:01:12 and run home in 1:58:48.
What are the five inputs?
These are the things that actually predict the outcome. Score yourself on each one, without rounding in your own favour.
| Input | The marker | Why it matters |
|---|---|---|
| Recent half marathon | 1:52 or faster, last 6 weeks | the closest real evidence you have |
| Weekly volume | 45 km (28 mi), 8+ weeks | buys the last 10 km |
| Longest run | past 30 km (18.6 mi), twice | where sub-4 attempts die |
| Course | flat, few turns, uncrowded | 3 to 6 min swing at this pace |
| Weather | dew point under 16 °C (61 °F) | up to 4% slower when warm |
The half-marathon marker is the strongest single signal, and the rule behind it is simple: double your recent half and add 8 to 12 minutes. For most club runners that lands closer than any watch prediction.
The volume marker is the one people argue with. Doherty and colleagues found training volume predicted marathon performance in recreational runners, and Vickers and Vertosick (2016) found weekly mileage improved prediction beyond race time alone across 2,497 runners. Volume is not there to make you fast. It is there so the pace you already have survives to 35 km.
How do I score myself?
Count how many of the five you meet.
| Inputs met | What it means | What to do |
|---|---|---|
| 5 | sub-4 is the right target | pace it evenly, hold 5:41/km (9:09/mi) |
| 4 | realistic, with a plan B | set 4:00, accept 4:05 |
| 3 | possible on a good day | start at 4:05 pace, decide at 30 km |
| 2 | not this race | target 4:15 and race sub-4 next time |
| 0 or 1 | finish well instead | 4:30 run well beats 4:00 walked |
The second row is the one most people are in, and the honest advice for it is not to abandon the goal. It is to have two paces in your head before the start, and to pick between them at 30 km rather than at 5 km.
Why do most sub-4 attempts fail?
Not on speed. On the last 8 km, and almost always for one of three reasons.
The first 10 km were too fast. At this fitness, 5:30/km feels identical to 5:41/km on fresh legs in a crowd. Two minutes of cushion bought in the first hour costs four in the last. Deaner and colleagues found most amateur marathon runners slow in the second half, men more than women.
The longest run was 25 km. The gap between 25 and 42 is not filled in by a taper. As one runner put it, _a taper is not going to magically give you 12 extra miles_.
The weather changed and the plan did not. A warm day is a different race. Adjusting the target on the start line is not giving up; it is arithmetic.
What should I do with a prediction from my watch?
Treat it as one of five inputs, not as the answer.
Watch predictions read your speed at a heart rate. They have no field for your longest run, which is exactly the input that decides this race. The race predictor here prints three published models so you can see how far apart they are, and the piece on why they disagree explains what each is actually computing.
If you want the splits for the day, the pace calculator gives them in both units, along with the pace your watch needs to show once it measures the course long.
And one number to carry with you: if you reach halfway more than 2 minutes 24 seconds ahead of 2:00:00, you are not ahead of schedule. You are borrowing.
Questions runners actually ask
- What half-marathon time means I can run sub-4?
- About 1:52, run in the last six weeks. Doubling a half and adding 8 to 12 minutes is the most reliable rough marker for club runners, and 1:52 doubled plus 12 is 3:56. A 1:58 half with the volume behind it can still do it; a 1:58 half without it usually cannot.
- How many kilometres a week do I need?
- Around 45 km (28 mi), held for at least eight weeks, is the realistic floor. People do it on less, and they are usually the ones who lose four minutes in the last 8 km. Volume buys you the last hour, not the pace.
- Can I do it if my longest run was only 25 km?
- Sometimes, and it is the single most common reason people miss by a few minutes. The gap between 25 km and 42 km is where sub-4 attempts die. Two runs past 30 km (18.6 mi) change the odds more than any speed session.
- Does the course matter that much?
- Yes. A hilly course or one with a lot of turns can cost 3 to 6 minutes at this pace. A crowded start can cost another one or two before you cross the line. Check the elevation profile before setting the target.
- What if it is hot on race day?
- Move the target. El Helou and colleagues showed marathon performance falls as temperature rises, and Ely found slower runners lose more than faster ones. On a warm day, sub-4 training is a 4:05 to 4:10 race, and chasing the original number is how it becomes 4:30.
Sources
- Vickers AJ, Vertosick EA. An empirical study of race times in recreational endurance runners. BMC Sports Sci Med Rehabil 8:26, 2016 primary
- Keogh A et al. Prediction equations for marathon performance: a systematic review. Int J Sports Physiol Perform 14(9):1159-1169, 2019 primary
- El Helou N et al. Impact of environmental parameters on marathon running performance. PLoS ONE 7(5):e37407, 2012 primary
- Deaner RO et al. Men are more likely than women to slow in the marathon. Med Sci Sports Exerc 47(3):607-616, 2015 primary
- Doherty C et al. Training volume and marathon performance in recreational runners. Eur J Sport Sci, 2020 primary
Changelog
- — First published.