Ironman Racing – A Pacing Plan

The faster you go the sooner you finish. Obviously pacing decides the outcome of an Ironman; the aim is to be as fast as possible, but too fast can be disastrous. Determining correct pace requires testing and practice during training and an appreciation of the importance of nutrition to sustain the effort. Ironman is about who can maintain their speed from start to finish.

Pace is a misleading target, heavily influenced by course conditions, what you are trying to control is our race effort. Perceived exertion rules with the support of heart rate, power and for the run, pace. Each of these give an indication of how hard you are working, but ultimately feel determines if that is appropriate. If it feels too hard then it is a risky strategy that continues to push.

Whatever measures are being used to guide your race you cannot blindly pick targets from the Internet. I’ve written about the importance of testing and race specific practice and this is when it is key. You need to use this process to establish target heart rates, wattages, swim or run pacing; then you need to practice to establish how they feel. This ensures you have a sense of the exertion you will manage on race day.

The Plan


The swim is based on feel, there is no opportunity to check splits or heart rate in the middle of the water. Challenging when a taper has you feeling fresh and adrenaline is flooding the body. It may be the shortest leg of the day, but mistakes made now will impact later. The objective is to swim at a strong, sustainable effort and importantly to use drafting to increase our speed.

The plan begins before the race with your start position being a critical element. For any athlete looking to set a good time and confident around packs I suggest an aggressive placing. Be realistic, but push to the leading edge of your swim performance. Faster swimmers will pull you along; join the group and if the effort is too high, drop back and join the next one. Done well you’ll gain free speed for the same work as a solo swim.

Never aim to break records in the first 400m. It is tempting, but from experience going too hard will lose you time throughout the day. Breathing is a useful guide – you should not be breathing like a sprinter, if you are back down. Focus on a controlled pattern, bilateral if possible, don’t feel desperate for oxygen.

Sight throughout, never rely on the navigation of others. You want to be in a fast moving group, not one heading to the wrong buoys. If the bunch is off course it may be better to jump ship, but bear in mind how hard bridging can be. Sitting in a draft can feel slow, it’s only when you move away you appreciate the work involved at that pace. Keeping an appropriate effort is important so leaving a bunch may involve slowing down.


There are more options to judge pace on the bike – chances are you have heart rate or power to supplement feel. The aim is to ride consistently, sustaining your efforts through the 180 kilometres; this is prime fuelling period, you want to reach the marathon with the energy to run. Pace needs to be controlled enough that you don’t overly fatigue and you can keep taking on nutrition.

A system of caps works well; based on training you define a target heart rate or power to warn when you are working too hard. Typically cap your race effort around 70% to 75% of your threshold, work as close to this as possible without crossing the line. Courses often present conditions that push you over this, I allow a secondary cap – around 90% to 95% of threshold – for those situations. When terrain forces you to work harder, the objective is to stay as far below this cap as possible.

Immediately after transition my heart rate is rocketing. I stay calm, don’t significantly slow and resist the urge to go harder. Power gives me a more accurate view on the work being done; I know in time my heart rate will settle as long as I don’t push now. Ensure it feels easy, slowly build effort over the first fifteen minutes till you’ve reached your cap. Once there, settle in and focus on eating. It will feel hard later on and you want to be ready to ride through the fatigue.


The cap system remains. My preference is to guide running with a mix of pace and feel, but heart rate is a useful tool. Similar to the bike the goal is to run consistently with the final 10km being an opportunity to push. Pace is controlled, a successful strategy ensures you at least sustain the effort until the finish line, if not pick it up.

Cap your run around 20 beats below your threshold heart rate or in terms of pace roughly 10% slower than marathon pace. This is where testing in training is vital – I utilise pace work in long runs and specific brick sessions to ensure I’ve chosen correctly. Whilst running may not be as significantly impacted as cycling by terrain the course may require a secondary cap. I am more controlled running hills than I would be cycling them, but allow heart rate within 10 beats of threshold.

Fatigue is high after hours of racing. It’s difficult to replicate this in training, choosing a run pace is the hardest part of your race strategy. A percentage of a test result that works in theory may not work after seven hours of activity. It is important to have practiced pacing goals, but also to be adaptable. You need to feel you can sustain the pace throughout.

For the first few kilometres running will seem easy and the pace may be high, remember you have to maintain this for a few hours. Hold yourself back and build to your cap; settle into your race pace, then focus on fuelling the remaining effort. As the marathon progresses you can reassess performance, 10km to go is the point to consider pushing. Nutrition and conservation of energy can be forgotten. Dig deep, you will make it to the finish.

Key Pacing Plan Points

  • Listen to your body throughout race day – back up feel with heart rate, power or pace.
  • Stay in control – judge your effort based on training and work to your abilities.
  • Do not cross threshold – if you do get below it as soon as possible. Don’t burn matches.
  • Remember nutrition – fuelling is vital, ensure you are taking in all you can.
  • Push to the finish line – as you approach the end you don’t need to conserve. Raise your game.

Ironman Training Library

From nutrition to pacing - a collection of CoachCox blog posts focused specifically on Ironman training and racing.