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How To Pace an IRONMAN Triathlon

Ironman runners

The best swim, bike and run pacing strategy for an IRONMAN 140.6 triathlon


An IRONMAN 140.6 involves a 2.4 mile swim, 112 mile cycle and 26.2 mile run. It will typically take you between eight and 17-hours to complete. Over such a long distance, your pacing strategy can make or break your race. This guide will show you how to get it right.

If you’re training for an IRONMAN 70.3, read this guide instead.

To realise your full potential during an IRONMAN 140.6 event, you need to switch off your competitive race-head and focus on preserving energy. No amount of “pushing harder” is going to make you faster. It’s more about economy of effort.

Imagine you’re driving 140.6 miles in your car, with a quarter tank of fuel left. You’re in a rush, but you’re also worried you might run out of fuel. The quickest way to get from A to B is to drive at the most economical speed. You want to reach your destination as quickly as possible, but without draining your precious fuel supply along the way. The same principle applies during an IRONMAN too.

If you pace yourself right, you’ll feel stronger and more mentally positive throughout the day. The first half of the event will feel relatively easy and you’ll probably wonder if you’re taking it too easy. During the second half of the race, you’ll start over-taking the people who started too hard. When you climb off the bike, you’ll still have some spring in your step for the marathon run.

You’ll even find it easier to digest your nutrition, because your body will be in a better state to process it. So you’ll have more energy as a result.

Below, we outline the best ways to pace yourself during an IRONMAN triathlon, broken down into the swim, bike and run sections.


Think of the swim as being a warm-up for the main event, rather than a race itself. Avoid the temptation to set yourself a target time for the swim. There are too many variables on race day to get this right. If you end up doing a swim that’s slower than your goal time it can lead to low morale and the temptation to catch up during the bike section.

Your IRONMAN swim should be done at a steady pace. There are several ways to pace yourself, including heart rate, pace and feel. From a practical point of view, using perceived exertion (or “feel”) works well – it saves you from trying to look at your watch.

Ironman Swim Perceived Exertion

  • Feels Like: Steady.
  • An intensity that feels like 4 out of 10 (where 10 is your hardest).​

Ironman Swim Heart Rate

  • Percentage of your Maximal Heart Rate: 60 to 70%
  • Beats Below Maximum Heart Rate: 30 to 50 beats.

Ironman Swim Pace

  • Take your fastest 100 m/y sustainable training pace, and add 10 secs per 100.
  • If you’re racing in a wetsuit, make sure you base your pacing strategy on your recent wetsuit training times. And vice versa.

Elite Age Group Triathletes

If you’re aiming for a sub-10-hour IRONMAN (men) or sub-11-hour (women) it’s a good idea to go a little harder in the first 300 to 400 meters of the swim. Aim for an intensity that feels like 8 out of 10.  This can help you get clear of the crowds and find similar or slightly faster swimmers to draft behind. You’ll save up to 10% of your energy for the 3.8km by swimming directly behind other swimmers. Either way, after the first few hundred meters, settle down to 5 out of 10 and preserve some energy for the long day ahead.


It’s vital that you pace yourself sensibly during the bike section. Once your legs get too sore from riding hard you have almost no chance of running well afterwards. There is no going back from this point – the run section will feel like purgatory. Don’t focus on being a hero by posting a super-fast bike split. There are no medals for a great bike-split followed by a disastrous run-split.

Riding at the right intensity takes discipline and courage especially when other people are overtaking you, but it really works. At around the 80-mile point you’ll notice people starting to drop off while you continue to ride strongly, overtaking people as you go. You’ll also find that pacing yourself sensibly helps you to digest your energy drinks and snacks far easier, which helps you maintain your energy levels going into the run.

Before we provide your pace guidelines, remember to base your IRONMAN race pacing strategy on recent data. You should do a Functional Threshold Power Test (which also incorporates a Heart Rate Threshold test).  Don’t be over-optimistic or guess your fitness. Measure it.

Power Meter, Heart Rate or Feel?

Use a power meter (if you have one) to pace yourself on the bike, with heart rate and “feel” as back-up measures. If you don’t have a power meter, just use heart rate and “feel” instead.

Aim to ride at a steady power output, rather than in bursts. Have plenty of easy gears, so that you can maintain your normal cadence and power output up the hills, without busting your legs.

Bike Pacing: 8 to 9-hour IRONMAN athletes

  • Power: 78 to 80% of Functional Threshold Power (FTP)
  • Heart Rate: 88-90% of threshold bike heart rate
  • Feel: 5.5 out of 10

Bike Pacing: 9 to 10-hour IRONMAN athletes

  • Power: 76-78% of FTP
  • Heart Rate: 86-88% of your threshold bike heart rate
  • Feel: 5 out of 10

Bike Pacing: 10 to 11-hour IRONMAN athletes 

  • Power: 74-76% of FTP
  • Heart Rate: 84-85% of your threshold bike heart rate
  • Feel: 4.5 out of 10

Bike Pacing: 11 to 12-hour IRONMAN athletes

  • Power: 72-74% of FTP
  • Heart Rate: 81-83% of your threshold bike heart rate
  • Feel: 4 out of 10

Bike Pacing: 12 to 13-hour IRONMAN athletes

  • Power: 70-72% of FTP
  • Heart Rate: 78-80% of your threshold bike heart rate
  • Feel: 3.5 to 4 out of 10

Bike Pacing: 13 to 14-hour IRONMAN athletes

  • Power: 68-70% of FTP
  • Heart Rate: 76-77% of your threshold bike heart rate
  • Feel: 3.5 out of 10

Bike Pacing: 14 to 15-hour IRONMAN athletes

  • Power: 66 to 68% of FTP
  • Heart Rate: 73-76% of your threshold heart rate
  • Feel: 3 out of 10

Bike Pacing: 15 to 17-hour IRONMAN athletes

  • Power: 64-66% of FTP
  • Heart Rate:  69-72% of your threshold heart rate
  • Feel: 3 out of 10


Did you realise that by the time you start the marathon run in an IRONMAN triathlon, you’ll have already been racing for between 5 hours 30 and 12-hours? You’ll be very tired and low on energy before you even start. And your pacing strategy needs to reflect that. An IRONMAN marathon is not like a normal marathon. The best outcome you can realistically expect is to maintain an easy or steady pace throughout.

For many people, a walk-run strategy is the best way to pace an IRONMAN run. Taking structured walk-breaks from the start can help you gain control over your fatigue levels. According to numerous surveys, you’ll also run up to 13 minutes faster for a marathon. For more information on marathon run/walk strategies click here.

To gauge your intensity on the run, use a combination of heart rate, pace and “feel”. None of these measures are completely reliable in isolation, because there are so many things that can affect them – such as wind direction, gradient and cardiac drift (an increase in heart rate due to heat stress).

So bearing that in mind, here’s how to set yourself a realistic pacing plan, using three different measures…

IRONMAN Run Heart Rate

You should start your Ironman run at 75 to 80% of your threshold heart rate. For example, if your threshold heart rate is 160 beats per minute, start running at 120-128 beats. Sounds too low, right? Keep this up until halfway and then you can increase your pace slightly if you feel fresh enough (but the chances are you won’t). You may even need to run/walk in order to keep your HR down.

IRONMAN Run Pace/Speed

If you know your threshold running pace (your current 1-hour race pace) you can use our online training zone calculator to estimate your IRONMAN run pace. Your IRONMAN run pace is at the lower end of Zone 2 or even into your Zone 1 pace. For example, if your threshold pace was 7:30 min/mile, your realistic IRONMAN pace would be around 9:25 min/mile. Although it depends on the route and conditions. You can test your threshold running pace here.

IRONMAN Run Perceived Exertion

Based on perceived exertion, your IRONMAN race pace should feel like a 2 or 2.5 out of 10 on the intensity scale. With 10 being your hardest effort. On a good day this might be described as being an “Easy” pace.

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In this guide, we’ve described how to pace the swim, bike and run sections of an IRONMAN 140.6. The take-home message is that economy and intelligent pacing are the best ways to succeed. Don’t leave it to chance or make it up on the day – measure your fitness and then devise yourself a pacing plan. It’s a seriously long event and your pacing strategy needs to reflect that.

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Phil Mosley (Coach & Founder)
Phil Mosley (Coach & Founder)

Phil is a recognised endurance expert who founded MyProCoach in 2010 to offer smart training plans that still leave quality time for your family, friends & career - complete with highly-rated coach support (he has sold over 40,000 so far). Learn more here!

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