How To Pace an IRONMAN 70.3

Swim, bike and run stronger with this IRONMAN 70.3 triathlon pace guide…

An IRONMAN 70.3 is the first step towards the world of long-distance triathlon. With its 1.9km swim, 90km bike and 21.1km run it’s an event that can take anything from four hours, right through to eight. These events are sometimes called Half IRONMAN or Half Triathlon.

So let’s say for argument’s sake it takes you five or six hours. That’s a LONG time to be swimming, cycling and running, and you’ll need a pacing strategy that reflects that. If you treat it like it’s an Olympic distance triathlon you’ll pay a hefty price later in the day.

Thankfully the advice in this feature shows you how to pace yourself properly so that you feel strong throughout. The secondary benefit of getting your pacing right is that it gives your body a fighting chance to process all the gels, bars and energy drinks that you consume during the event. So not only will this pacing strategy help you to race faster, but it will also keep you more energised along the way. Let’s start with the swim…

IRONMAN 70.3 Swim Pace

During the first 300 metres of the swim, you can find yourself swimming hard, without even trying. Once you find your place in the group and hopefully get in the draft zone of similar-level (or slightly faster) swimmers, ease down to your target intensity. If you’re a nervous swimmer, start off steady and stay out of harm’s way.

There are several ways to pace yourself, including heart rate, pace and Rate of Perceived Exertion (RPE). However, from a practical point of view, using RPE (feel) works well – it saves you trying to look at your watch.

There are several ways to pace yourself, including heart rate, pace and RPE. From a practical point of view, using RPE (feel) works well – it saves you trying to look at your watch.

Rate of Perceived Exertion

  • First 300 metres, your intensity in Z4 and feel 7 to 8 out of 10 (feeling hard)
  • After the first few minutes, intensity should then dial down to a moderate High Z3 to Low Z4. Feeling like 6 to 7 out of 10 (where 10 is your hardest)

Max Heart Rate

  • First 300 metres, your intensity should be 87 to 93% of your Maximal Heart Rate
  • For the remainder, 80 to 87%
  • Beats Below Maximum Heart Rate: 20 to 40 beats


  • Take your fastest training pace for a 100, and then add 5 secs per 100 to get your IRONMAN 70.3 swim race pace
  • If you’re racing in a wetsuit, make sure you base your pacing strategy on your recent wetsuit training times (and vice versa)

Check our Triathlon Race Pace Calculator to help guide your swim pacing strategy.

Transition 1:

Don’t sprint like Usain Bolt and build up lots of lactic acid in your legs. This is a five or six-hour race, and you should not be out of breath. Jog into transition. Be smart in transition – and save your legs for later.

IRONMAN 70.3 Bike Pace

Use a power meter (if you have one) to pace yourself on the bike, with heart rate and RPE (feel) as backup measures. If you don’t have a power meter, just use heart rate and RPE instead. Aim to ride at a consistent power output with the difference between your average power and normalized power being as close to zero as possible. In other words, no spikes in power for hills or sprints. If it’s a hilly route, you might benefit from a compact chainring and a rear cassette with a 30 or 32-tooth chainring. This should give you enough gears to maintain a nice steady power output without spikes, on all but the hilliest routes.

It is important not to base your pace strategy on the bike split that you would ‘ideally like to do’. Use the pacing guidelines below and be realistic with your goals.

Power Output

IRONMAN 70.3 target > Suggested target % FTP

  1. Sub 5 hours > 83 to 84%
  2. 5 to 6 hours > 80 to 83%
  3. 6 to 8 hours > 77 to 80%

Threshold Heart Rate (THR)

IRONMAN 70.3 target > Suggested target % Bike THR

  1. Sub 5 hours > 88 to 92%
  2. 5 to 6 hours > 84 to 88%
  3. 6 to 8 hours > 81 to 85%

Rate of Perceived Exertion (where 10 is the hardest)

IRONMAN 70.3 target > Suggested target RPE (feel) Zone

  1. Sub 5 hours > 6 out of 10 Mid to High Z3
  2. 5 to 6 hours > 5 out of 10 Low to Mid Z3
  3. 6 to 8 hours > 4/5 out of 10 High Z2 to Low Z3

Check our Triathlon Race Pace Calculator to help guide your bike pacing strategy.

Riding at the right intensity takes discipline and courage, especially when other people are overtaking you. But it really works. Get it right and later, on the bike course, and then on the run, you’ll be passing those who passed you. You’ll also find that you can better digest your nutrition, helping you maintain your energy levels going into the run. You will run faster as a result of pacing yourself properly on the bike, and you’ll feel fresher and more energised.

Transition 2:

Jog. Be smart, don’t waste time. Save your legs for the run.

IRONMAN 70.3 Run Pace

If you paced the swim and bike sensibly, you’re in with a fighting chance of running to par. Either way, you’ll still be tired by the time you hit T2. After all, you’ll have been racing for 3 to 6 hours already. So don’t expect to run fast like it’s an individual half marathon. Realistically you should be aiming for an intensity that’s similar to, or slower, than your full-marathon pace.

Threshold Heart Rate (THR)

IRONMAN 70.3 target > Suggested target % Run THR

  1. Sub 5 hours > 90 to 92%
  2. 5 to 6 hours > 87 to 89%
  3. 6 to 8 hours > 85 to 87%


IRONMAN 70.3 target > Suggested target % Threshold Run Pace

  1. Sub 5 hours > 90 to 91%
  2. 5 to 6 hours > 87 to 89%
  3. 6 to 8 hours > 86 to 87%

Rate of Perceived Exertion (where 10 is the hardest)

IRONMAN 70.3 target > Suggested target RPE (feel) Zone

  1. Sub 5 hours > 5 out of 10 Low Z3
  2. 5 to 6 hours > 4 out of 10 High Z2
  3. 6 to 8 hours > 3.5 out of 10 Mid Z2

Check our Triathlon Race Pace Calculator to help guide your run pacing strategy.

Using all three of the methods (RPE (feel), HR and pace) is best as none of them are entirely reliable in isolation. Many variables can affect them, such as wind direction, gradient and cardiac drift (an increase in heart rate due to heat stress). The downsides of starting too fast are far greater than the downsides of starting too slow.

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IRONMAN 70.3 Strategy

My final tip is to make sure you treat your half IRONMAN with respect. Use accurate and recent data to plan your pacing strategy, rather than guesswork. As well as getting your pacing right, you need to think carefully about nutrition. The principles in this IRONMAN nutrition blog will help you. For more training advice check out our Half Ironman plans here.

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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