Pacing for a Hilly Ironman

Ironman racing is simply a matter of managing pace and nutrition over the course of a day. You work at an intensity you know you can hold all day long. It might take concentration, at times it might be hard, but you’re sure you can manage that effort. You’re certain because you’ve followed my advice and practiced it in training: the work feels familiar. Despite the simplicity so many go wrong and struggle through the marathon.

The bike is where the biggest errors occur. You feel fresh from a taper and set out at too hard. It feels good, at least for a couple of hours. Eventually it bites and the only thing that can happen is you slow. Once down that route it’s hard to recover. Putting a cap on intensity can save you from walking the run. It doesn’t matter if the cap is defined by power, heart rate or perceived exertion; what’s important is you stick to it.

Capping intensity is easy. You see a power or heart rate over your cap: you ease up. If it feels harder than it should: back off the pace. Train for this so you know what it feels like and what numbers work. Simple!

It’s straight forward until you hit the hills. Unless you chose to race in Florida or Western Australia they’ll be some climbing. St George, Lanzarote, Nice: the right (or perhaps wrong) course and the ascents are significant. The bike route may necessitate working beyond your self-imposed cap. How do you pace a race when the hills take you out of your comfort zone?

Affect of profile on bike heart rate

Immenstadt wasn’t an Ironman, but contained enough brutal climbs to make 130km feel like one. Climbs were rarely long, but they were decidedly steep. My normal cap of 150bpm frequently became the minimum needed to crest a hill. Bursts of intensity take a lot out of the legs; I was well aware my quads could be suffering by the run. Downhills allow some recovery, but not enough to compensate for frequent surges. Besides easing up too much downhill is giving time away.

The German course was two laps – the first slightly longer than the second – both with significant climbs. I attempted to hold back on the first and push the second harder. A strategy that works well. Early on people rode by, but I caught most of them before the run. A test ride had confirmed it would take more than 150bpm on the climbs so I set myself a secondary cap. When there was no way to get below 150 (short of getting off) I’d ensure I stuck below 160.

I broke my rules on the first hill! Excitement as spectators lined the road. Fortunately we lost the crowds and I saw sense. For the rest of the race I was more controlled. I rode flats and downhills like any other race, keeping the effort in control and the heart rate under 150. I worked slightly harder than average up shallow hills. Intensity was close to the limit, but remained under the primary cap. On the steep climbs I had to cross the line and work harder. I emphasised keeping heart rate and effort as low as possible.

There was always the potential for a hill to necessitate breaking the secondary cap. A bit steeper still and it’d be out of my control. The caps are guidelines: set points to keep it simple. What I’m seeking to do is spend the shortest amount of time working above my sustainable effort. I know it will happen, but aim to minimise its impact on the race. In the same respect I avoid easing up on the downhills. A generally even pacing strategy with slightly more work on the uphill sections.

At times it felt slow. Athletes came riding by, but controlling my effort lets me sustain my pace for longer. Power up the hills early and they’d feel like mountains later. Surges in effort come at a price if I crossed that line too many times my race would suffer. Holding back well in the first lap let me gamble on pushing the second. It was a risk, but trusting in my run fitness I was willing to take it. I had to be sure I could handle a few more hours racing even with the extra efforts.

The rules are identical for the run: have intensity caps. The numbers or feel may be different, but the principles remain the same. Above this intensity there’s a high risk you’ll slow before the line. Below it there’s the chance to pick things up and finish strongly. I judge my performance by pace, but I’m aware of its limitations on a hilly course. I’m trying to control the work I do; 6:30 miles are significantly harder on a 5% grade. My preference is for perceived exertion. I’ll strictly keep my efforts under control until I’m approaching the end.

As with cycling I allow for an increase in exertion on hills, but limit how hard I go. Downhills present an additional challenge. There is free speed, but the eccentric loading does more damage to tired legs. I’ve rarely ‘raced‘ down hills; I’ve used them to settle my heart rate after a climb. A moment to ease intensity, recover and pull yourself together for the remaining miles. However tempting it is to fly down them I hold back and keep my run together.

On a good day there are no rules for the final few miles. Just push, you’ll make it to the line. Even then pacing on hills can still matter. Out in Kona a couple of miles from the finish I pushed from the bottom of the final rise to Palani. A short climb, but after 24 miles I felt every inch of it. I went too early and too hard; by the top my legs were gone. Had it been more than a mile to go things would have turned very ugly! Late in the day, but a clear demonstration that going too hard comes at a high cost. It wouldn’t have gone so well if I’d ten miles to go.

Athletes tend to let hills and harsh conditions psych them out. Everyone faces the same course on the same day. A flat course can be just as challenging as a mountainous one if you pace it correctly. Both should be raced at the hardest effort you can sustain for the duration. The hills will slow you, but they’ll slow everyone. You may spend longer racing and that does mean holding back a little more, but so should everyone. Controlling and managing your effort over the day so you finish strongly will serve you well.

Hilly or flat, it’s the way you manage your race that will make the difference.

Ironman Training Library

From nutrition to pacing - a collection of CoachCox blog posts focused specifically on Ironman training and racing.


  • Interesting point about not ‘racing’ down hills. The eccentric loading can certainly take a LOT out of your legs if you pound your way down, but I’d argue that there are some pretty massive gains to be made here relative to your competition and gains, that if you are competitive you’d be foolish to ignore! I also believe that you can run fast downhill without any massive eccentric loading too!

    For example – The majority of smart racers will suggest if you have an out and back bike leg with a huge headwind one way and a massive tail wind the other – if you want to take advantage you want to make your gains in the headwind. The extra effort here will go further than if you lay the hammer down in the tailwind, everyone motors then!

    I’d say that the opposite (depends on which way you look at it) is true for running, but applying the same logic. There are much greater gains to be made on the downhill in running, because its much more technical and as a result people tend not to be very good at it. In a race between any average runner, and someone who has good all round technique, its plain to see where the gaps really open up, why not exploit the basic fact that there is generally more speed to gain on a downhill, and less speed you can lose on the uphill the steeper a hill gets.

    With swimming its another story…but thats not what we are talking about.

    Come on Russ, enter yourself into some trail marathons, and I’ll prove it to you 😉

  • I suppose it depends on what you term racing. I left it in quotes because it’s not the same as run racing the legs are already fatigued. There’s route from my house with a steady ascent I can run it up in 5 minutes or down for 4 without much difference in heart rate. It’s strictly about managing intensity at no point do you sustain periods above your cap until you’re close to finishing. You do this because the race is about sustaining at optimal pace to the end.

    Interestingly on the bike issue I am suggesting you work harder against resistance, but again within your limits. My experience in windy races with a headwind is most athletes over do it into a head wind and under do it with a tail wind. I remember racing in Port Mac Half in those conditions with the wind behind me I struggled to hit my target watts whilst sailing past people. Sure they were going fast, but I was going faster without exceeding my limits. On the second lap the now tired athletes were much slower both out and back.

    I think specifics of marathon and trail racing don’t translate fully to IM marathon I’m cautious about over doing it for free speed when you’re approaching the limits of your metabolism. In a marathon I know I’ll only have an hour to go when energy may become an issue. Trail marathons obviously make the dynamics change though at least you start it fresh.

    Sorry bit rushed will see if I can find the power data to support this.

  • I suppose. I think we are on slightly different tacks here though.

    I was more suggesting where I think the best gains can logically be made which I think holds for running whether it be an ironman or trail run, purely because of the nature of technique in running and its variance with up/downhill.

    Your blog merely brought up the idea that in training/racing I think its logical to make the gains where you are going to get the biggest bang for your buck, whether it be down to physics, technique, or what your competitors are doing, it all counts. Downhill running i think is probably one of those areas, as is weighting your effort into a headwind vs tailwind, and for swimming making yourself streamlined (so you are faster when there is the least resistance in your stroke)

    I certainly don’t disagree with your points on caps on intensity though which should be adhered to, and almost certainly explains why you were mowing down your competitors at Port Mac Half.

  • Here’s an interesting couple of papers on variability of pacing in Time Trials – or basically testing variable pacing strategies against constant ones. The conclusions are that going 5% harder than average uphill and 5% easier than average downhill works best. However the note at the end is that it was difficult for subjects to judge that variability. My experience has been that most go too hard against resistance and end up going too easy without it. The problem is that ultimately the too hard sections take a lot out of them and the too easy sections are insufficient for full recovery. They’re accumulating additional fatigue and using up glycogen reserves faster than intended. The Ironman then adds the additional difficulty of a marathon to follow – where preserving energy can be key.

    I guess I’m wary of encouraging and attitude of racing – it’s not the same as a 5K or even a marathon in that respect. You race within the limits of your abilities and most are at those limits already. I prefer language that suggest control of the situation over ones that encourage a more aggressive approach. I like to feel I’m playing a very careful game when I race – I could potentially go a bit harder, but I believe it’s better to save it. That’s not always the case I attacked the hills on the second lap in Immenstadt gambling on my run fitness. Similarly in Kona this year I decided given I had no idea what would happen on the run I’d approach it like there was no problem! Didn’t pay off in the latter case!

    Ultimately there’s a cap on what you can do whether you realise it or not, being aware of them at all points in the race gives you the freedom to choose to vary pace more. I of course suggest whatever strategy you think you use you practice heavily in training so your sure it works for you. If you haven’t raced down hills much I’d save testing how it works for you till late in the race.

    Always the problem with general advice – each individual needs to identify and use a strategy that works well for them. I’ve outlined a pretty safe options, but even then anyone thinking of using it should test it out in training.

  • Warren mason

    I think I agree with Andy on the downhill running theory. During my 15 year break between my 2 Tri ‘careers’ I did a whole lot of fell racing (well for 7/8 years anyway). After analysing heart rate data I found it drop by 10-15BPM on the downhills when just following my ‘natural’ pace judgement which also seemed to be a similar pace to my race peers in each respective race – i.e. I hardly lost or gained places. I then started to push harder on the downhills on fell races (and any road races that also had hills) to try and keep my HR at my race threshold. Obviously, the terrain didn’t always allow this but I found that where it did I gained significant distance (& places) without too much detrimental effect. Trying to really relax and maintain a very high leg speed helped counteract the effect of eccentric loading. Occaisionally I would be re-passed by the odd runner but I would estimate this to be only about 1 in 10. So, I still use it now in all races and feel it’s ‘free’ speed or at least the extra effort expended is worth the distance gained. Again, one to try in training with a HRM but ‘it works for me’.

  • Guess you can’t win them all!

    I don’t entirely disagree – and I suppose I’m not really saying go slowly and let your heart rate drop through the floor. I probably do allow some easing off and recovery if I’ve gone harder up the hill, but not that much. I’ve never really made a conscious effort to speed up down a hill. With my run style cadence remains the same throughout all that really changes is leg lift. Down hills I can pick up some speed without changing how I’m running.

    I’ve thought on this topic more since writing this one and also reading some of the pacing research in time trialling. What strikes me is that whilst a variable pacing strategy is likely to be faster there were questions abotu the ability of subjects to correctly assess pacing.

    We’re back to my standard recommendation: practice it. You’ve found you can handle the downhills well and gain advantage. You’ve tested it out. Everyone should be finding that out before they adopt a race strategy.




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