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How to Train for an IRONMAN Marathon

BY Ryan Riell

Running a marathon after swimming for 2.4 miles and biking 112 miles is very different than running an open marathon. Learn how to set your zones correctly and use pacing strategies to train correctly. 

While a marathon is 26.2 miles, how you approach it depends on if you are solely running, or if you have a swim and bike beforehand. Two of the most common questions are, “How do you compare an open marathon to an IRONMAN marathon” and “What does my run training for the IRONMAN marathon need to look like?” Both are great questions and essential for putting together a training program to accomplish your goals on race day.

Using the Right Metrics

The first key is to make sure that your running pace is based around a physiological value, such as Lactate Threshold (LT). Heart rate (HR) is not an output metric, it’s an input metric. Basing run training on HR (while actually running, as in looking at the HRM) is better than nothing, but it’s not going to put you in the best position possible when training and on race day. Remember, HR is subject to a lot of variable such as temperature, hydration, mood, nutrition, etc… which can lead to too much variability to use accurately in training as anything other than a guide.

Using your running velocity at LT (vLT) to determine running zone paces (min/mi) is an OUTPUT metric, meaning it’s what you’re putting out while training and racing. It’s the equivalent of using power on the bike.

Setting Training Zones

Lets use two sample athletes, the first having run their IRONMAN marathon in 3:15 and the second who ran 3:44. I typically assume that an athlete who runs an IM marathon under 4 hours can safely subtract 20 minutes and get their open marathon time. For athletes over the 4 hour mark, it might get up closer to 30 minutes.

The table below is calculated from the TrainingPeaks Pace/Speed Zone calculator using Joe Friel for Running. It shows all the relevant data to include estimated vLT1 and training zones based off those.

The training for each of these athletes needs to be based off their “open” marathon time and associated vLT, not their IRONMAN marathon time. If we use vLT, our training zones will be far more accurate since there are now physiological variables attached to them.

The 3:15 IM marathon pace of 7:27 is in middle of zone 2 (7:05-8:01) for zones that are set based on the 2:55 marathon time and associated vLT.

The 3:44 IM marathon pace of 8:33 is in middle of zone 2 (8:10-9:15) for zones that are set based on the 3:24 marathon time and associated vLT.

Intensity of Long Run Training

Next is how fast to pace your long run. Remember the main reasons for a long run are time on your feet and building endurance. The physiological benefits we are seeking include an increased stroke volume, increased mitochondrial density and capillarization as well as strengthening the connective tissue in the lower limbs. These benefits occur most effectively in zones 1 and 2, when you’re between 60-75% of max HR (look after the run) or 55-75% of VO2max.

As you increase your intensity up into the “tempo” or zone 3 range, you are starting to stress different energy systems. Adding some zone 3 work into longer runs is a very wise strategy, especially for someone who is running around 3:30 or less for a marathon and/or if performance is a goal. Running for 2 hours at that intensity is doable, but the muscular damage and extended recovery might not be worth it.

Tempo runs by themselves can reach the 90-minute range (with warm up and cool down) and provide some tremendous benefits! The question you need to answer, do you want quality or quantity?

Here are some sample “tempo” workouts, which can be converted into longer runs by adding to the warm up and cool down.

Steady Tempo Run

  • Warm Up: 15 minutes in zone 2 (use the full zone)
  • Main Set: 40-60 minutes in zone 3
  • Cool Down: 15 minutes in zone 2 (using the full zone again)

If the second athlete in the previous example got an hour in at the slower end of zone 3, that would be close to 7.5 very high quality miles.

Tempo Intervals

  • Warm Up: 15 minutes in zone 2 (use the full zone)
  • Main Set: 3×20 minutes in zone 3 with a short recovery
  • Cool Down: 15 minutes in zone 2 (using the full zone again)

This adds up to the same basic numbers above, but I would argue, you will get a higher quality of running, more time in the faster end of zone 3, if you break that time up and add in a short recovery.

Threshold Repeats

  • Warm Up: 15-20 minutes in zone 2 (use the full zone)
  • Main Set: 2-4 x 2-miles or 6-8 x1-mile in zone 4 with a 4’/3’/2’ easy jog recovery
  • Cool Down: 15-20 minutes in zone 2 (using the full zone again)

This workout will add in some more high-end running that is marathon specific.

Pacing for an IRONMAN Marathon

Now that we have established the differences between an IRONMAN marathon and an open marathon, as well as the proper pacing for your run training, we can look more closely at pacing during the IRONMAN. The pacing for race day should be based off your projected IRONMAN marathon time, not your open marathon time.

In the examples above, the first athlete can run a 2:55 open marathon, but is looking at a 3:15 at IRONMAN. Their pacing needs to be selected based on the 3:15 time, which would put them between 7:52 and 8:54 min/mi. Looking at the second athlete, their proper pacing on race day should be between 8:56 and 10:06 min/mi. These running paces will put both athletes in zone 2, which is sustainable for an IRONMAN marathon.

If the athletes used the open marathon paces, they would ultimately end up in zones 3 and 4 based on the IRONMAN marathon goal time. The first athlete’s zone 2 would drop down to 7:05 to 8:01 min/mi, which puts them well into their IRONMAN-based zone 3 and even into the lower ends of zone 4. The same is true for the second athlete that is looking to run a 3:44 marathon.

Training for a marathon, either open or in an IRONMAN, requires a mix of endurance, strength and speed. By working with your pace rather than heart rate, and training to the specific needs of each event, you can reach your goal.



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Ultimate Ironman Training Guide

Training Guide

This guide is designed to be used as you train for an IRONMAN triathlon, with in-depth information on every part of the process. Each chapter is packed with tips, workouts, and insights from triathlon coaches, to give you all the tools you need to succeed.

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About Ryan Riell

Ryan Riell is a nationally recognized expert in applied exercise physiology and biomechanics in the realm of triathlon and endurance sports. Riell has two masters degrees, the first in exercise physiology and biomechanics and the second in organic and biological chemistry. He is a former elite coach at TrainingBible Coaching and former USA Triathlon High Performance Team head coach and team director. Ryan can be reached by email at ryan@ryanriell.com, or through his website at www.ryanriell.com.