Running intervals for Ironman?

Ironman, December 12, 2016

Ironman athletes regularly ask if there is any point in running hard intervals for an event that is so long. Well there is a lot of point and how far and how fast they should be completed may well surprise you.

Running intervals for Ironman?

After a recent article about using interval training for improving running race times, an athlete left a comment along the lines of ‘ This is all very well, but it won’t help if your doing Ironman’. The idea that, the IM run is a long slow effort and so that is how I should complete my running training, seems to be a common view among age group IM athletes. But this ignores what we know about how the human body adapts to training stimulus. Indeed, Racesnake would contend that, high intensity interval sessions should be part of every Iron distance athletes training plan. Why?

The Science

First let’s be clear, there is very little research into the optimum training and racing methods for ultra endurance events but we do know a fair bit about how to train for aerobic endurance sport. Iron distance races are ultimately just massive aerobic events and so it is fair conclude that improving the physical variables that improve performance in other aerobic events, will improve performance in Iron distance triathlons.  

At this point, before I talk specifically about the run discipline, it is useful to point out that much of the success of an athlete in Iron races is due to the athletes ability to complete the bike with an effort/speed ratio that allows them to arrive at the run without excessive fatigue. In other words for most people if they want to run faster in IM then get better at the bike section!

That said we know that running at high intensity is an effective way to improve several key physiological variables that are closely linked to improved performance. Improving run economy, lactate threshold and vV02 max is widely accepted to lead to improved running performance in races up to marathon distance. As these things essentially contribute to an athletes aerobic endurance it is reasonable to assume they will improve performance in IM, as it is primarily and aerobic endurance event. Now before you say it, yes running a long way slowly will also improve these variables, it just won’t do it anywhere near as effectively and it’ll take much more time. Studies by Billat et al have shown that high intensity interval training raises run economy, lacate threshold and vV02 max (as well as improving actual race times) significantly more than either long steady running or running at threshold.  It is also worth noting that high intensity running is also more likely to improve your aerobic and anaerobic capacity. 

How hard?

Well this, for many Iron athletes, is the kicker. Science has shown us that the most effective intervals are hard, much harder than you might think. Most research agrees that running at between 85-90% maximum heart rate or a pace somewhere between your 10km- 1500m P.B, is the most effective intensity for interval training.  A typical session may be:

15x1min @ 3km pace with 1min jogging recovery

12x400m @ 3km pace with 200m jog recovery

5x1km @5km pace with 60s recovery

At these high intensities athletes spend a long duration running at V02 max, improving fitness, and develop nuero-muscular co-ordination, helping improve run economy. Whilst these things will directly improve your running, the improvements in V02 max will also contribute to your general endurance in all three aspects of the Ironman. 


These sessions are hard, very hard. You need to make sure that subsequent sessions are easy enough to allow adequate recovery and this may take up to 48hrs. This type of high intensity training fits well into the scientifically proven ‘polarised’ or ’80/20′ model. So, if you want to improve your Ironman splits don’t ignore hard intervals, just make sure your easy sessions are easy but those hard sessions, well they should hurt!

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