Negative Split
Running or racing the second half of an event faster than the first half, the opposite of starting fast and fading.
A negative split means covering the second half of a race faster than the first half. In a marathon, that might mean running the first 21.1km a little slower than goal pace and the second 21.1km a little faster, finishing stronger rather than surviving to the line. It's the direct opposite of the far more common pattern among untrained pacers: a fast, adrenaline-driven start followed by a steady fade as fatigue catches up, sometimes called a positive split.
Negative splitting isn't the same as running conservatively for its own sake. It's a deliberate pacing strategy built around a specific idea: start at an effort that feels almost too easy relative to what the field around you is doing, hold it with discipline through the middle of the race, and use whatever's left in the second half to close faster rather than merely hang on.
Why it's a common pacing goal in endurance racing
Coaches and experienced athletes favor negative or even splits because the alternative, starting fast and fading, tends to produce a worse total time for a given fitness level, not just a worse-feeling race. Going out too hard burns through glycogen and anaerobic capacity at a rate the body can't sustain for the full distance, and once that debt is created, it doesn't get repaid mid-race.
It's also more forgiving of the small errors that happen in every real race. Starting conservatively and adjusting up as data comes in, how you actually feel at 10km, at the halfway mark, at 30km, leaves room to correct. Starting aggressive and hoping to hold it leaves none. That's a large part of why elite marathon performances, world records included, tend to show slight negative or close to even splits rather than dramatic front-loaded pacing, even when the field around the leaders is going out faster.
The physiological and psychological case for it
The physiological argument centers on fuel and heat management. A negative split conserves glycogen for the second half of a race instead of spending it early on a pace that isn't sustainable, and it reduces the cardiovascular and thermal strain that builds when effort consistently outpaces what the aerobic system can support. Held over hours rather than minutes, that difference compounds: an athlete managing effort conservatively in the first half typically arrives at the final quarter of a race with meaningfully more capacity left than one who's already spent it.
The psychological case is just as real, even if it's less often discussed. Passing tired competitors in the final kilometers is a genuinely different experience from being passed while hanging onto a fading pace, and it reinforces exactly the discipline that produced it: restraint early paying off late. Built on a race pace that's been properly tested rather than guessed, that restraint is the pacing plan working as intended, not caution for its own sake. Physiological reserve plus a psychological lift at the point in a race where motivation usually matters most explains why negative splitting keeps showing up as a goal across distances, from a 10K to a full-distance Ironman marathon, and not only among elite athletes with nothing left to lose.