Pacing The Ironman - Part 1

What is the best strategy for pacing the Ironman Triathlon?

The most common answer is to aim for an even or negative split for each leg, and be conservative on the bike. I have been wondering if this is really true, after all, most people do not achieve this. In fact, the majority of people slow down as the race progresses. Is this good, bad, or indifferent? What should be the used as the overriding measure, heart rate, power, speed, or percieved exertion? What are the advantages and disadvantages of different strategies?

What do triathletes actually do in the Ironman and how does it affect their result?

Pre-race the most common strategy does appear to be to aim for a negative split. Many athletes judge this by heart rate, often aiming to keep below a certain threshold for the first part, and then above a certain rate later in the day. These intentions are common, but the reality is that most athletes do not achieve this. Whatever the reasons are, the majority of triathletes in an Ironman slow down as the race progresses. A study performed at Ironman Western Australia over two years looking at the pacing, heart rates, cadence and power outputs of a number of riders showed while cadence and heart rates remained relatively constant, there was a significant slowing of the athlete's paces and force output throughout the 180km ride. Of particular note is that most riders had a larger power output over the first 30km of the ride than compared to the rest of the race.

This slowing down has also been observed in ultradistance cyclists. It has been reported that there is a 10% decrease in heart rate for every 10 hours of cycling. The authors of this study also suggested that an Ultra-endurance Threshold exists that is approximately 70%HRmax. Yet in 20-40km cycling time trials the evidence points to a non-linear power output that typically shows a higher than average output during the first portion, a drop during the middle section, particularly in the the 3rd quarter followed by the highest power outputs being achieved towards the end of the time trial. This curve remains fairly constant for races less than 2 hours in duration. The Ironman fits somewhere in between these two examples, and has to consider that is made up of three disciplines as well.

Which leads us to consider how does one leg affect the other? Swimming has been shown to affect the cycle portion of sprint distance triathlons. Based on a stand alone time trial, it has been observed that completing the swim leg of a sprint distance triathlon at 100% of the time trial velocity results in a slower cycle leg when compared to swimming at 80-85% or 90-95% of the swim TT velocity. The cycling versus running relationship is significant. There is a host of evidence showing that a relatively fast bike leg can result in a slow run leg (or walk leg even).

Should you increase the intensity during for certain conditions of the race, such as hills and wind. It has been shown in races/time trials of around 20-40km that increasing the effort into a headwind or up a hill by 5-10% can result in a faster overall time. The basic reasoning is that you will take more time travelling uphill or into a headwind than on the flat, downhill or with a tailwind. However, it is unclear whether this can be extrapolated to Ironman distance.

What about short increases in intensity? Will putting a surge to get a clean run to the drink station, or clear the crest of a hill do more harm than good? The answer looks like it that a few surges, when compared to a steady approach will make the race harder. A study comparing steady-state cycling with a variable pace effort, but at the same average power output over 140min, followed by a 20km time trial show some important results. The variable paced effort resulted in increased blood plasma lactate concentrations and ....

My Thoughts

So after looking at the research, taking my own and other people's experiences into account, I have come up with a plan. It needs to be remembered that this plan is based on my current fitness level and goals for the Ironman Australia in a bit over 6 weeks. Plus the training over the next three weeks may slightly affect this plan. Of course, like all good plans, there is the possibility that come race day, it may have to be thrown out the window. Since I have made this such a long winded post, I'll put the plan into my next posting.


Abbiss CR. Quod MJ. Martin DT. Netto KJ. Nosaka K. Lee H. Surriano R. Bishop D. Laursen PB. Dynamic pacing strategies during the cycle phase of an Ironman triathlon. [Journal Article. Research Support, Non-U.S. Gov't] Medicine & Science in Sports & Exercise. 38(4):726-34, 2006 Apr.

Neumayr G. Pfister R. Mitterbauer G. Maurer A. Hoertnagl H. Effect of ultramarathon cycling on the heart rate in elite cyclists. [Journal Article] British Journal of Sports Medicine. 38(1):55-9, 2004 Feb.

Palmer GS. Borghouts LB. Noakes TD. Hawley JA. Metabolic and performance responses to constant-load vs. variable-intensity exercise in trained cyclists. [Clinical Trial. Journal Article. Randomized Controlled Trial. Research Support, Non-U.S. Gov't] Journal of Applied Physiology. 87(3):1186-96, 1999 Sep.

Peeling PD. Bishop DJ. Landers GJ. Effect of swimming intensity on subsequent cycling and overall triathlon performance. [Journal Article] British Journal of Sports Medicine. 39(12):960-4; discussion 964, 2005 Dec.

Tucker R. Bester A. Lambert EV. Noakes TD. Vaughan CL. St Clair Gibson A. Non-random fluctuations in power output during self-paced exercise. [Journal Article. Research Support, Non-U.S. Gov't] British Journal of Sports Medicine. 40(11):912-7; discussion 917, 2006 Nov.


  1. I'll be interested to see how you adapt this to your plan. I imagine a long ride followed by long run session would give some adaptation. I know my (few) tri run legs always felt like walk legs, however I could never swim well enough to make the bike leg hard ;)

  2. All that great info, then you make us wait?

    The timing of this was perfect. I've been wondering how I am supposed to approach this. I'm certainly worried about being able to maintain an appropriate bike speed, so that I can still run....or hobble in my case.

  3. wow..interesting man. wish you all the best for ironman.wuhu~

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  7. Wow! Thanks for sharing the research and information.


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