Race split times
If you run negative splits this means that you run the second half of the race quicker than the first. Positive splits means that you run the second half slower than the first.
Probably, yes. Most athletes perform better if they run the second half of a race slightly faster than the first half. In general, marathon runners should aim to spend 51% of their time on the first half of the race.
If you choose a gradually changing pace, the race splits calculator assumes your pace gradually increases (for negative splits) or gradually reduces (for positive splits) over the race.
The calculation works by fitting a quadratic curve:
percent of time = (2-4*ø)*(percent of distance)^2 + ((4*ø) - 1)*percent of distance)
where ø is the percent of the distance to be covered at half way.
If you choose even-paced halves, the race splits calculator calculates two speeds, on the assumption that you will speed up (for negative splits) or slow down (for positive splits) at exactly half way.