The marathon after 180 km on the bike is a different beast: core temperature, walk-run strategy, and why heat hits the run harder than the bike.
The question that separates a good long-distance day from a catastrophic one: "How do I run a marathon on legs that already swam 3.8 km and rode 180 km?" The honest answer: differently from any other marathon of your life.
In short-course triathlon the run is 5 or 10 km — your body manages that even with suboptimal pacing. At long-distance, 42.2 km follow half a day of pre-fatigue, and your core temperature keeps climbing while you run it: in a study at the Ironman World Championship in Kona, athletes' core temperature rose from an average 36.6°C at race start to 38.55°C by the end of the marathon — a fever spike that would send you straight to bed with a cold. And that overheating was still present 60 minutes after the finish.
That explains why heat hits the run leg harder than the bike: analyses of professional races show that high temperatures and altitude impair running performance the most — more than any other segment. The marathon is the moment where every mistake of the day shows up.
After 180 km on the bike, running often feels deceptively easy — the legs are numb, not recovered. Athletes who start too fast out of transition pay later with far more time lost than they gained early on. Stick strictly to your planned pace, even if it feels too slow.
Because your core temperature keeps rising through the marathon and heat hits the run leg hardest, cooling isn't a side note. Use every aid station: ice water on the neck, wet sponges, cold drinks — every tenth of a degree saved counts over 3–5 hours of running.
Race-data analyses from long-distance events suggest that short, planned walk breaks at aid stations often make the second half of the marathon faster than stubbornly running through until you break down. Plan this beforehand as a strategy — not as a last resort once your legs are already failing.
Somewhere between kilometer 25 and 35, most athletes hit a point where everything feels wrong. That's normal, not a sign something is broken. Have a mental plan ready — a focus point, a mantra, the next aid station as an intermediate goal.
From kilometer 35 on, it's no longer about pace, it's about stability. Whoever is still running instead of walking here has almost always paced more conservatively than the rest of the field. Focus on form and breathing, not the pace display.
Watch for signs of overheating later in the marathon: stopping sweating, confusion, dizziness, goosebumps despite the heat. These are warning signs to take seriously — don't push through, alert medical staff immediately.
Because core temperature builds up over the whole marathon, cooling once at the start isn't enough — cool consistently at every station, especially in the second half.
Set yourself a fixed rule before the race: "at every aid station I walk, drink, cool down, then keep running." This removes the decision from a moment when your head isn't thinking clearly anyway.
A trick experienced finishers use: they mentally split the marathon into four 10-km blocks rather than 42 km at once — each block has its own small goal, easier to grasp than "30 km to go".
Because your legs feel numb rather than exhausted right after the change in movement pattern. That's exactly what tempts many into starting too fast — the bill usually comes between kilometer 20 and 30.
In a study at the Ironman World Championship, athletes' core temperature rose on average from 36.6°C to 38.55°C by the end of the marathon — and stayed elevated even an hour afterward. Cooling during the run is therefore not optional.
Not necessarily. Race-data analyses suggest short, planned walk breaks often make the second half of the marathon faster than stubbornly running until a complete breakdown. Planned often beats stubborn here.
Because running in high heat is demonstrably more impaired than cycling — professional race data shows heat and altitude reduce running performance the most. On the bike, airflow provides extra cooling; running lacks that effect.
Long-Distance Triathlon: Transitions and Race-Day Logistics