People who have done a 70.3 and are considering a full distance usually ask whether the training doubles.
It does not. A well-prepared middle distance athlete might train ten hours a week. A well-prepared full distance athlete might train thirteen or fourteen. That is a thirty or forty percent increase, not a hundred.
But the training is the smallest of the changes, and the ones that matter get much less attention than they deserve.
What Actually Changes
One: fuelling stops being optional and becomes the event
This is the biggest difference and it is not close.
A 70.3 takes most people five to seven hours. You can complete one on a fairly casual fuelling approach, take in less than you should, and finish anyway because your glycogen stores just about cover it.
A full distance takes twelve to fifteen hours. There is no version of that where stored fuel is sufficient. You will consume somewhere between 800 and 1,200 grams of carbohydrate across the day, while moving, in the heat, with a gut that is receiving reduced blood flow.
Athletes who step up from half to full and do not fundamentally change their approach to fuelling are the ones who spend the marathon walking and vomiting. The half did not teach them, because the half did not need to.
Two: the marathon is a different event from the half marathon
Running 21 kilometres off a 90 kilometre bike is hard. Running 42 kilometres off a 180 kilometre bike is categorically different.
In a 70.3 you can hold a pace that hurts and get away with it, because there are only ninety minutes of it. In a full, an intensity that is fractionally too high at kilometre five is unsustainable by kilometre twenty-five, and the collapse is total rather than gradual.
The Ironman marathon is a pacing and fuelling event. It is barely a running event at all for most of the field.
Three: pacing tolerance narrows enormously
In a 70.3, riding slightly too hard costs you minutes on the run.
In a full, riding slightly too hard costs you the race. The bike intensity band that produces a good full-distance run is narrow, and it feels absurdly easy for the first two hours. Athletes coming from the half consistently ride their full at half-distance intensity, and it is the single most common step-up mistake.
Four: the day contains problems the half never produced
Saddle sores. Numb hands and feet. Chafing in places you did not know could chafe. Sunburn accumulated across ten hours. Needing the toilet. Weather changing twice. Your feet swelling out of your shoes.
None of these appear in a six-hour race. All of them appear in a fourteen-hour one, and each has a solution that has to be worked out in training rather than discovered on the day.
What Changes in the Training
Concretely, the differences that matter.
- The long ride extends from around three hours to five or more. Not for fitness. For your back, neck, hands and saddle contact, and to practise five hours of eating.
- The long run extends modestly, from around ninety minutes to two or two and a half hours. It should not extend beyond that.
- Bricks get much more serious. A thirty to forty-five minute run off a five-hour ride is the most valuable session in a full-distance build.
- Fuelling gets rehearsed as a skill, at race intensity, with race products, until you know your tolerable rate to the gram.
- Recovery weeks become non-negotiable rather than advisable, because the accumulated load is higher for longer.
What Does Not Change
Your weekly structure. Your swim volume, largely, because the swim is a small fraction of the day either way and 3.8 kilometres is not a fitness problem for anyone who has done 1.9. Your intensity distribution. Your strength work.
People imagine a completely different life. It is mostly the same week with a much longer Saturday.
Should You Step Up?
My honest test is not fitness. It is three questions.
- Did you finish your 70.3 running, or walking? If walking, the answer is another 70.3 done properly first.
- Do you know your carbohydrate tolerance per hour, from testing? If not, solve that before entering.
- Can you find one five-hour block, most weekends, for six months, without it damaging something that matters more? Be honest.
If all three are yes, you are ready. If not, another season at the half distance is not a delay. It is the preparation.
The Bottom Line
The training goes up by about a third. The fuelling demand roughly doubles. The pacing tolerance halves. And the day introduces a set of physical problems that a middle distance never revealed.
Train for the fuelling and the pacing. The fitness was mostly already there.
