You've trained for months. On race morning you feel fresh after your taper, the crowd is loud, and the first kilometre flies by 20 seconds faster than planned. It feels easy. That moment is where many races are lost.
What the data shows
Big-city races publish split times for every runner, and researchers have used them to study pacing on a huge scale:
- An analysis of more than 1.7 million recreational marathon runners found that recreational runners are much less good at choosing and holding the right pace than elite athletes – many start too fast and slow down sharply at the end.
- In data from the Chicago Marathon, half of the runners who "hit the wall" (slowing down by a third or more in the second half) had run their fastest 5 km at the very beginning. The fastest finishers, by contrast, varied their pace by less than 5% between the two halves.
- Runners who ran with or near a pacing group were several times more likely to run even splits.
- Experience helps: runners with more previous marathons and higher training volumes slow down less in the second half.
These studies are about the marathon, where mistakes are punished hardest, but the same pattern shows up in half marathons, just less dramatically.
Why going out fast costs so much
Running faster than your sustainable pace early on burns carbohydrate faster and builds fatigue that you can't fully undo. The seconds you "bank" in the first kilometres are usually paid back with interest later – often several times over.
The goal: even, or slightly faster at the end
For most runners, the best plan is an even pace, or a second half that's a touch faster (a "negative split"). Practically:
- Know your goal pace – realistic, based on recent training and races, not on hope.
- Make the first 1–2 km deliberately controlled, a few seconds per kilometre slower than goal pace. Crowds, adrenaline and fresh legs will make goal pace feel too easy. Trust the plan.
- Settle into goal pace for the middle of the race. This is where your training does the work.
- Decide in the final quarter. If you feel strong with 5 km to go in a half marathon (or 10 km in a marathon), that's when to push.
Tools that help
- Pacing groups. Find the pacer for your goal time, or the one just slower, and stay with them early.
- A pace band or a note of checkpoint times. Compare with the official kilometre markers – your watch often drifts in cities and between tall buildings.
- Effort, not only pace. On hills, aim to keep the effort steady rather than the pace: a little slower uphill, a little faster downhill.
- Start in the right corral. Starting too far forward means being swept along too fast.
A note on heat and wind
Warm weather, wind and hills all cost time. On a hot day, adjust your goal before the start rather than discovering in the second half that it was too ambitious.
The bottom line
Your race is rarely won in the first kilometre, but it is often lost there. Start a little slower than feels right, settle into your pace, and save your push for the last part of the race.
Sources
- Smyth B. Fast starters and slow finishers: a large-scale data analysis of pacing at the beginning and end of the marathon for recreational runners. J Sports Analytics. 2018. doi:10.3233/JSA-170205
- World Athletics: Marathon mathematics – Barry Smyth's analysis of recreational runners (2016). worldathletics.org
- Swain P, Biggins J, Gordon D. Marathon pacing ability: training characteristics and previous experience. Eur J Sport Sci. 2020. doi:10.1080/17461391.2019.1688396
- Deaner RO, Carter RE, Joyner MJ, Hunter SK. Men are more likely than women to slow in the marathon. Med Sci Sports Exerc. 2015;47(3):607–616.