The frustrating thing about a bad run split isn't that you went too hard on the run. It's that you often didn't.
The damage was done earlier — in the water, on the bike, in decisions that felt completely reasonable at the time. You have a TSS budget for the run. Eat into it before T2 and the distance doesn't change. The course doesn't get shorter. You just have less left to cover it with.
Nobody talks about blowing up on the swim. For a full IRONMAN, that's almost justified — 3.8 kilometres at a controlled effort is rarely where races are lost.
A 70.3 is different. Thirty minutes of hard open water effort, cold water, adrenaline, bodies everywhere. CSS — your critical swim speed, the pace you can sustain without accumulating debt — is easier to breach than your bike threshold when race-day chaos takes over. Most athletes have no idea it happened. The swim felt hard but manageable. The first unplanned withdrawal has already cleared, and the bike hasn't even started.
There's a TSS range that predicts a good IRONMAN run. Exceed it and the marathon doesn't just get harder — it gets exponentially harder. The relationship isn't linear. A 10-point overshoot doesn't cost you 10 points worth of run performance. It costs you significantly more, because fatigue compounds.
And it compounds from multiple directions at once. The lactate you carried out of the swim. The surges on the bike that the average power didn't capture. The temperature that climbed through the afternoon. The humidity you didn't fully account for. Conditions you couldn't control and some you didn't see coming. Each one makes the next one more expensive. By kilometre 20 of the run you're not dealing with one problem — you're dealing with the accumulated interest of every decision made since the starting gun.
Most athletes can see their TSS on the bike — the number is right there on the head unit. What they don't have is a target that accounts for all of it. Without that, the number is just a number.
It's rarely the whole bike leg that breaks the run. It's a handful of moments. The climb where you went with the group. The technical section where you accelerated out of every corner. The headwind section where you pushed more power to hold speed rather than accepting the drop.
Individually, none of them feel significant. Collectively they shift your TSS by more than you'd believe, and because they're scattered across 90 kilometres of riding they never show up as a red flag in any single metric. The average looks fine. The damage is real.
Most race plans are actually three separate plans loosely stapled together. A swim pace. A bike IF. A run target. Each one built in isolation, with no model for how the first affects the second, or how both affect the third.
A plan that holds up works differently. It starts with the run and works backwards. What can your legs absorb from the bike and still run to potential? What does that mean for your bike effort? What does the swim need to look like given your fitness and the conditions? These aren't independent questions — they're the same question asked three different ways. The answer isn't just a finish time — it's a complete pacing strategy across all three disciplines, where every target is connected to the next.
This is what Keiro builds. Not discipline by discipline, but as a single connected system — because that's what a triathlon actually is.
None of this is meant to make racing feel complicated. It's meant to make it feel manageable — so that when the gun goes off, you're not guessing. You already know how the race should unfold. You just have to go and do it.
Find your race and start planning.