Every other swimming event is one stroke repeated, so pacing strategy is relatively uniform throughout — the IM is fundamentally different because a swimmer must transition between four biomechanically distinct strokes in a single race, each with its own optimal pacing, which is exactly why split analysis is so much more valuable here than for a straight freestyle event.

The breaststroke leg in particular is where many IM races are decided — it's the slowest stroke and the one where technique breakdowns under fatigue cost the most time, so coaches watch a swimmer's breaststroke split relative to their other legs specifically to judge whether their all-round stroke technique (not just their fitness) is holding up under race pressure.