How to avoid a DNF in Ironman: essential race day strategies

Entered an Ironman and worrying about hitting the wall and not completing? James Witts explains strategies that will help you avoid a DNF and complete in style

Ironman athlete on the bike leg

As Jodie Stimpson’s coach Darren Smith once told me, “Confidence derives from confidence.” And if you don’t train, you’ll always have doubts because competence will remain absent. It’s the same with mental toughness – train at least eight hours each week (ideally more if you’re looking to chalk up some results), including one long ride, and you’ll feel confident that you’ve accumulated a good level of fitness.


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But fitness, as many iron athletes who’ve bonked can tell you, is only one piece of the long-course jigsaw. Hitting the wall often comes down to poor pacing and/or a poorly planned nutrition strategy. 

When it comes to pacing, the swim should almost be a joy. Okay, that’s a touch hyperbolic but, for many, the 3.8km is about falling into a nice easy rhythm, keeping clear of trouble and, ideally, drafting the athlete in front of you to conserve energy. 

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On the bike, which can take some athletes up to 8hrs, pacing becomes more strategic and more important. This is where it’s worth splashing out on a power meter. You can race to a wattage you know is sustainable – around 65-80% of functional power threshold (for most people) – and stick to it like a Gomez to a Brownlee! Or if you’re using a heart rate monitor, predominantly stick in Zone 2. This equates to around 60-70% of your maximum heart rate. That might not sound huge but it taps into huge fat reserves, which will preserve precious glycogen (carb stores) for the run.

Setting off too fast on the run will result in a DNF. This is where negative-splitting comes in, which is where you run the second half of the run faster than the first. Another proven way of preventing bonking is to walk/run, where you employ a certain ratio that you’d have practised in training.

Ironman Run Strategies

As for race nutrition, consuming 60-90g of carbohydrates per hour is ideal, in whatever form you feel comfortable with. This could be fluid, bars, gels and/or blocks. You should try to mix things up on the bike with ‘real food’. Something like a jam sandwich or rice cake is easily digested and not as sweet as manufactured bars. Just remember that it’s easier to digest bars on the bike, not the run, and to feed at regular intervals. You could set your HRM to remind you to eat/drink every 15mins.

Ironman nutrition: plan for success and nail the fuelling

Finally, heed the cerebral advice of Chrissie Wellington: “I used to have personal mantras to inspire me, including Rudyard Kipling’s If. I’d also break sessions and races down into manageable sections and, of course, learning to hurt in training was vital so that I could reach those depths when it came to a race.”



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