Glossary
Negative split
Running the second half of a race faster than the first. A 2% split is modest and achievable; most amateur marathons are run the other way round.
What it is
Second half quicker than the first. In a marathon at 4:00:00, a 2% negative split means 2:01:12 out and 1:58:48 back.
It is rare in amateur fields. Deaner and colleagues studied 14 marathons and found most runners slowed, men more than women.
| Split shape | First half | Second half | Common outcome |
|---|---|---|---|
| even | 2:00:00 | 2:00:00 | the plan |
| negative 2% | 2:01:12 | 1:58:48 | strong finish |
| positive 5% | 1:56:00 | 2:10:00 | the usual disaster |
What it is not
It is not slow running. The first half is barely different from even pace: 72 seconds across two hours, which is 6 s/km (10 s/mi). That margin is the whole difference in most sub-4 marathon attempts.
It is also not a guarantee. Starting slower does not create fitness. It stops you spending fitness you do not have.
What moves it
- The first 5 km. Almost the whole decision.
- Crowd and adrenaline. Both push you faster than planned.
- Heat. Warm days punish a fast start harder.
- Course profile. A downhill first half hides the error.
When to ignore it
Ignore the target on a course with a big net climb in the second half. Judge on effort instead.
Ignore it in a 5K, where the race is short enough that a hard, even effort is the whole strategy.
Sources
- Hanley B et al. Pacing profiles of senior athletes at the World Athletics Championships. Front Sports Act Living 4:964905, 2022 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
- March DS et al. Age, sex, and finish time as determinants of pacing in the marathon. J Strength Cond Res 25(2):386-391, 2011 primary