More races are lost in the first mile than in the last. The gun goes, the crowd surges, the legs are fresh from a taper, and a pace that will cost you ten minutes at the finish feels like nothing at all. By the time it starts to hurt, the decision was made half an hour ago.
Pacing is the one part of racing that is entirely under your control, and it is worth more than most people think. Here is what the three ways of running a race do to the same fitness.
The fast start finishes last
Three runners, one goal pace. Going out fast buys a few seconds a mile early and costs minutes late. Starting a shade conservative and finishing strong is the fastest way through the same distance.
- Fast start
- Even
- Negative
Illustrative profiles against a four-hour marathon goal. The fast start runs the first third about four percent quicker than goal and pays for it with a ten percent fade; that shape is what most positive-split race data looks like, though the size of the fade is individual.
The three ways to run a race
Positive split. The first half faster than the second. This is how most amateur races are actually run, and it is almost never a plan. It is what happens by default when the start is exciting and the goal pace is optimistic.
Even split. The same pace throughout. Nearly every distance world record from the mile to the marathon has been run close to even, with the second half within a percent or so of the first. This is the strategy that extracts the most from a given fitness and the one to aim for when you know your fitness well.
Negative split. The second half faster than the first, usually by a small margin. In practice this means starting a shade conservative and finishing strong. It is slightly less efficient than a perfect even split in theory, but it is far easier to execute, because it builds in a margin for the most common error. For most runners in most races, this is the target.
The pattern behind all three is that the cost of running too fast early is not symmetric with the benefit. A few seconds a mile banked in the first third is paid back with interest in the final third.
Why going out fast costs more than it saves
Three things happen when you run the first miles faster than your fitness supports, and none of them can be undone by slowing down later.
You spend glycogen faster. The relationship between pace and carbohydrate use is not linear. A pace a little above your sustainable one draws disproportionately on limited glycogen stores, and in a marathon that is the difference between fuelling to the finish and hitting the wall at 20 miles.
You accumulate lactate you cannot clear. Above your second threshold, lactate production outpaces clearance. Going out fast puts you above that line while you are fresh, and the debt does not go away when you drop back to goal pace. The heart rate zones guide covers where that line sits.
You heat up. Core temperature rises faster at a faster pace, and the body's response is to slow you down whether you agree or not. This is why the fast start punishes warm-weather races most.
Add the mechanical cost of running fresh on a taper, with a stride that is slightly longer and bouncier than your trained one, and the first mile of a race is genuinely the most dangerous mile in it.
Choosing a goal pace you can hold
Pacing strategy only works if the pace itself is right. An even split at a pace you cannot hold is just a slower version of the fast start.
The best evidence is a recent race. Convert it with the race time predictor, and be honest about the fatigue factor: a 5K result predicts a marathon well only if your mileage supports the marathon, and the default exponent flatters runners who are stepping a long way up in distance.
The second-best evidence is training. If your goal marathon pace has never felt controlled in a long run with a race-pace segment, it is probably not your goal marathon pace. The training paces guide covers how each training pace relates to race pace and what "controlled" should feel like at each.
Then turn the goal into a number you can act on with the running pace calculator, and check it against the neighbouring paces on the pace chart so you know what a few seconds slower per mile looks like at the finish.
A goal pace has to survive a bad day
Set the goal for the fitness you have, not the fitness you hoped to build. If the taper went well and the day is cool, you will find that out in the second half, which is exactly where you want to find it out.
Setting your splits, by distance
The shape of a good race is the same at every distance: a controlled start, a long even middle, a finish that uses what is left. What changes is how long each part is and how much margin the start needs.
| Race | First section | Middle | Finish |
|---|---|---|---|
| 5K | First kilometre at goal pace, no faster | Hold | Last kilometre as hard as you can |
| 10K | First 2K at goal or a touch slower | Hold | Last 2K building |
| Half marathon | First 3 miles 5 to 10 seconds per mile slower than goal | Hold | Last 3 miles at or under goal |
| Marathon | First 5 miles 5 to 15 seconds per mile slower than goal | Hold to 20 miles | Whatever is left |
Two things to notice. The margin at the start grows with distance, because the cost of getting it wrong grows with distance. And the "finish" in a marathon is not a sprint; it is the last six miles, and the goal there is simply not to slow down. A marathon where the final 10K matches the pace of the middle 20 miles is an excellently paced race.
A pace band, a wrist list of split times at each mile or kilometre, is the simplest tool for executing this. Build it from the pace calculator's splits, adjusted for the conservative opening miles, and check it at every marker rather than trusting how the pace feels.
Adjusting on the day
The plan is built for conditions you cannot control. When they change, the pace changes with them, and the runners who accept that early beat the ones who hold the number and blow up.
Heat. Above about 15°C, expect goal pace to cost more. The warmer it is, the more you slow, and the effect compounds through the race. Start conservatively and treat the goal as the ceiling, not the plan.
Wind. Running into a headwind at goal pace costs far more energy than running with it saves. Ease back into a headwind and take the tailwind as free speed, rather than fighting for an even split against the air.
Hills. Run hills by effort, not by pace. Aim for a steady heart rate or a steady breathing pattern up the climb, and let the pace fall; you will recover it on the descent without the cost of having surged.
Heart rate drift. Over a long race, heart rate climbs at a constant pace as you dehydrate and heat up. A heart rate that reaches your threshold number at 15 miles is a warning, not a target. If you race by heart rate, set the ceiling with the heart rate zone calculator and read it as an early sign that the second half needs to be respected.
Common mistakes
- Running the first mile on adrenaline. The single most expensive minute of any race. Check the watch at the first marker and slow down if it is fast, however good it feels.
- Chasing a group. The runners around you at the start are mostly running the fast start. Let them go; you will pass most of them later.
- Holding the number in the heat. An even split at goal pace on a hot day is a plan for a positive split. Adjust the goal before the race, not after the fade.
- Surging on hills. Surging uphill to hold pace spends far more than it saves.
- Sprinting too early. The finish is the last 10 percent of the race at most, and in a marathon it is really the absence of a fade. A kick at 35K is usually a walk at 40K.
- Using a goal from a different fitness. The time you ran two years ago, or the time you would like, is not a pacing plan. A recent race or a rehearsed long run is.
The part a pace band cannot tell you
A pace plan is only as good as the goal it is built on, and the goal is only as good as the training that produced it. The band cannot know whether the long runs supported this pace, whether the taper delivered the freshness it was meant to, or whether today's heart rate and sleep say that the goal is conservative or optimistic.
That judgement, made from your own data, is the coaching. Vaast makes it: it sets a race goal from the training you actually did, builds the pacing plan around it, and tells you before the start whether the day looks like one to hold the number or one to respect it.