Breaking the 4 Hour IRONMAN Run


For many people setting a time target for an IRONMAN, a common one is to complete the run-leg in a time below 4 hours. Like in a normal marathon, this is no easy feat. Below we look into what it actually takes to do a sub-4 hour run-leg and make some suggestions on how to realise that goal.

Outline the Goal

Ignoring the fact there is a swim and a bike before the run for now, let's break the goal down: 42.2km in 4 hours is 10.5km/hour or just over 5:41min/km for the four hours. In reality, if we are looking at walking maybe one minute through the aid stations (say 12 on the course, we actually need to run a sub-3:50 marathon with 12 minutes walking). This means we need to be able to hold sub 5:30min/km, probably closer to 5:20min/km for the run to make up the time and get around the course in under four hours. 

What does that look like for my Running Profile?

Extrapolating from the above times, for a runner to be capable of those times on a normal non-triathlon day, that would mean being able to run 5km in about 23:30, 10km in about 49 mins and a half marathon sub 1:50. These times equate to a threshold running pace of 5:00-5:06mins/km.

So what does that tell us? That means that in training or in a practice running race, we need to be capable of hitting those numbers over the shorter distances to achieve a run time of sub-3:50 for a marathon distance run. Ideally, we can run faster than those numbers, which would give us more of a fighting chance.

Instead of looking to a fresh performance at a running race in order to work out your target IRONMAN run splits, the other option is to do a triathlon "training race". In such a race, if you are able to run a 23:30 off the bike in a Sprint Tri, a sub-49 mins off the bike in an olympic triathlon or a sub 1:50 half IRONMAN run...then you will know that you are on track to being capable of running a sub-4 hour IRONMAN run leg. Those times are off the bike and therefore really are your race paces, and as a general rule of thumb would indicate that you are likely to go sub four hours after a 180km bike.

How do we apply that to IRONMAN?

The IRONMAN run though has two separate components: the run (obviously!) and everything that went before it!

An important factor to bear in mind is that everyone reacts to running off the bike differently.

Some people's PB's are off the bike, others struggle a lot. Many athletes that I have trained can get very close to their standalone PB's and others tend to struggle. This can come down to many factors, including: over-biking, under-fuelling, poor pacing strategy, under-training, being unprepared or poor kit choice etc. 


There once was an old adage that works well as a general rule of thumb. Take your standalone marathon time and add 30 minutes; or add 10%. This means we need to look at about a 3:30 standalone marathon to dip below 4 hours, indicating that a threshold running pace of around 4:35-4:45 mins/km is needed in order to achieve a sub-4 hour IRONMAN run split.

The Icing on the cake

In a nutshell, if you want to run a 4-hour marathon off the bike, then you need to be ready to arrive at T-2 as run-fresh as you possibly can in order to run at your estimated race pace potential! Without adequate swim and run training in your legs, you will struggle. You need to be fit in all three sports to come close to your potential. Make sure you have a good bike fit, make sure you have your nutrition dialled in, make sure you have trained effectively for the event and make sure you know how to pace yourself. Fundamentally you need to ensure that your training is effective. To run fast in a triathlon, especially in an IRONMAN, everything else needs to fall into place. No matter what you may think, leaving out an element of good luck, good training routine, good training attitude and preparation will give you the best possible chance of achieving that sub four-hour goal!

As a side note, to give yourself the best chance of a good overall IRONMAN (as well as any other distance triathlon) time, you have to consider the race as a single, cumulative best-effort, not three separate races. By doing that you will achieve your best overall performance.

Good luck!