Ironman race-day: how to pace each leg

If you want to run rather than crawl across the finish line in your next race, you need to stretch out your energy reserves, says Joe Friel

Credit: Al Bello / Staff / Getty images North America

The two most important things to get right on Ironman race day are pacing and nutrition. Mess up either and the good times are over.


Fuelling your Ironman is a complex subject (turn to issue 248 of 220), so for now we’re concentrating on pacing – the key to making sure you’ve got the energy reserves to last all day in this toughest of races.

How to pace the Ironman swim

There are two strategies for the swim. The first is for those athletes who are competitive in their race categories and want to come out of the water with the leaders.

They’ll need to start fast, perhaps even going anaerobic for a brief stint, and then settle into a sub-threshold effort on other swimmers’ feet. Be warned: this strategy is dangerous. You could easily build up a lot of acid in your muscles.

The second pacing strategy is for the Iron-athlete looking to race a fast time while letting category placement take care of itself. Start at the pace and effort you intend to hold for the entire race while looking to always swim on others’ feet, passing when they fade.

Whichever pacing strategy you choose, rehearse and refine it in training. If possible, do some open-water swims with training partners to work on starts, drafting and navigation.

Sub-1hr session: Perfect your Ironman swim pacing

How to pace the Ironman bike leg

The bike is the key to Ironman triathlon success. The most common Ironman pacing mistake is to over-exert in the first 30mins of the bike leg. Go too fast while you’re taking on fluids and calories and your stomach will bloat. This is when the age-group athlete most needs to have a precise pacing plan and stick to it.

Hold back while staying in zone two for the first 30mins.You’ll be passed by athletes who are going too fast, but remind yourself that you’ll see them again later when you pass them.

Avoid zone three for all but the steepest of hills, and only touch on zone four if there’s an exceptional pay-off for doing so. This is rare. Never see zone five at this stage. A power meter is the best way to manage intensity.

Pros, especially the men, often race very fast at the start of the bike leg to keep the competition in sight, which is highly motivating, while benefiting from the slight draft of a fast-moving, albeit spread-out, group. They’ll be in zones three and four, perhaps even five, for a considerable time in the first two hours of the race, so will need to develop a nutrition plan that considers the potential for digestion slow-down that comes with such high-intensity effort.

This can greatly complicate their race and basically means that their nutrition needs become more concentrated as the bike portion progresses. If you’re not planning to finish on the pro podium, avoid this strategy.   Long rides in the 12 weeks up to race day should focus on your pacing strategy. Make it second nature so that you don’t have to think about it at the start of the race.

The Ironman bike leg: how to stay focussed for 180km

How to pace the run leg

Nearly all athletes have to start the run at less than goal pace and gradually speed up over the first 5km. Going out too fast is less likely than on the bike due to fatigue, but it happens. Holding back as you start the run will allow you to run a steady and manageable pace later on.

Be sure to save something in reserve for the last few kilometres. For fast Ironman athletes, the time to start running at high effort is with 10km remaining, but hardly anyone can do it because they’re fatigued from the bike.

The Ironman run isn’t fast. It’s slow even for the pros. If it wasn’t for the previous few hours of swimming and riding, you could run your Ironman pace nearly all day.

So fast intervals in training are of no value. Instead, do some short runs immediately after all of your long rides in the last 12 weeks with an emphasis on proper pacing. These need only be 15 to 30mins long; your weekly long run being in zone two.

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General Ironman pacing advice

Conserving energy at the start of each leg, especially the bike, will ensure that you can push yourself later on. If you make a mistake, make it on the side of going too slowly rather than too fast as you start each discipline.


You must make decisions about your pacing strategies at least eight weeks in advance of the race in order to rehearse and refine them. Then on race day, simply ignore what is going on around you and focus entirely on your own pacing plan. Do this – and get the nutrition right – and you’ll do well.

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