Running a negative split means finishing the second half of your run faster than the first half. It’s one of the most reliable ways to get the best results. Whether that’s in the 5k, 10k, half marathon or marathon. Why negative splits work: Lower risk of blowing up. Going out too fast is number one mistake in races. Stronger finish: Passing people late boosts confidence and performance. How to run a negative split, core rule for all distances: First half of the race: Slightly slower than goal pa