Even, positive, and negative split strategies
Pacing a distance swim comes down to how speed is distributed across the race. An even split holds a near-constant pace throughout, which tends to be metabolically efficient for many middle and longer distances. A positive split starts faster and slows later, common when adrenaline drives an aggressive opening. A negative split deliberately swims the second half faster than the first.
Even or slightly negative pacing is often favored for longer events because going out too hard raises blood lactate early and can force a costly slowdown. Very short sprints are an exception, where swimmers go close to maximal from the start.
Matching pace to distance and individual
The best pattern depends on event length, the swimmer's strengths, and tactics in a head-to-head race where positioning matters as much as the clock. Pacing also interacts with start and turn quality, which can mask or exaggerate split differences.
This is general educational information about pacing patterns rather than an individual race plan, which should be developed with a coach and informed by the swimmer's own time trials.