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

This is the only time in the race when you should go above 6 out of 10 intensity – and only at the start. Aim for 8 out of 10 intensity initially and use the first 300 metres of the swim to find your place in the group and hopefully get in the draft zone of similar-level (or slightly faster) swimmers. After a few minutes, you should be able to ease back down to 6 out of 10 intensity and maintain that right through to the end of the swim. If you’re a nervous swimmer, start off at 6 out of 10 and stay out of harm’s way.

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. You still need to be smart in transition – but save your legs for later.

IRONMAN 70.3 Bike Pace

Use a power meter as your first guide, with heart rate as a backup. If you don’t have a power meter you can use heart rate and feel.  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.

Sub 5 hour Half IRONMAN Athletes:

  • 83 to 84% of your threshold power output (FTP).
  • 88-92% of your threshold heart rate
  • Feels like 6 out of 10 intensity.

5 to 6 hour Half IRONMAN Athletes:

  • 80 to 83% of your threshold power output (FTP).
  • 84-88% of your threshold heart rate
  • Feels like 5.5 out of 10 intensity.

6 to 8 hour Half IRONMAN Athletes:

  • 77 to 80% of your threshold power output (FTP).
  • 81-85% of your threshold heart rate
  • Feels like 4.5 to 5 out of 10 intensity.

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 or slower than your full-marathon pace.

Sub 5 hour Half IRONMAN Athletes:

  • 90-92% of your threshold heart rate
  • 90-91% of your 1-hour race pace
  • Feels like 5 out of 10 intensity.

5 to 6 hour Half IRONMAN Athletes:

  • 87-89% of your threshold heart rate
  • 87-89% of your 1-hour race pace
  • Feels like 4 out of 10 intensity

6 to 8 hour Half IRONMAN Athletes:

  • 85-87% of your threshold heart rate
  • 86-87% of your 1-hour race pace
  • Feels like 3.5 out of 10 intensity
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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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