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This is a question that coaches are often asked, especially by those newer to Ironman racing, and my answer is typically: You can do a marathon before an Ironman, but you definitely don’t need to. Yes, I get that there’s a marathon within an Ironman, but beyond that, a marathon and an Ironman marathon are less similar than you’d expect, both in terms of training and race-day experience.
Let’s start by looking at training. For a standalone marathon, you’re likely going to do four to six runs each week. For an Ironman, you’re probably only including three weekly runs (plus a fourth run off the bike in some weeks). Focusing on the weekly long runs, for a standalone marathon you’re typically building toward a few 20-mile runs before race day. While approaches can vary for Ironman training, often you build toward a longer run of 2 to 2.5 hours, with the focus being more about time and less about distance covered.
If you’re wondering why there’s such a big difference in training strategies (given that you still have to run 26.2 miles either way) then remember that when you’re training for an Ironman, you’re training swim-bike-run rather than simply developing run fitness. Your run volume is likely less than half your total weekly training volume, but you are also developing cardiovascular fitness through swimming and biking. Your bike fitness in particular both supports and contributes to your overall run fitness. In marathon training, however, run fitness is predominantly built by running.
Beyond the training, the race-day experiences also have some substantial differences. A standalone marathon requires a lot of discipline for the first seemingly easy six to 10 miles, earns you some strong middle miles at a solid effort level, and then insists on a ton of grit to maintain your pace over the final 10K. This generally means that the discomfort and mental battle within a marathon are limited to the final six to 10 miles. Contrast this with the Ironman marathon, which has zero easy miles, insists on a ton of grit from the first step, and is simply a continuation of the discomfort and mental battle that began miles and miles ago on the bike. On a good Ironman day you might be gifted some strong middle miles at a solid effort level, but those are never guaranteed.
Ultimately, the experience of training for a marathon differs substantially enough from the experience of training for an Ironman that the first doesn’t necessarily prepare you for the second. Similarly, the experience of running a marathon doesn’t really prepare you for the experience of running an Ironman marathon. Because of that, I don’t think you need to do a marathon before an Ironman. But there are some reasons that you might want to do a marathon before your Ironman.
If you’re looking to develop a substantial base of run fitness prior to beginning your Ironman training, running a marathon can be a great way to accomplish that. Or, if you feel that completing a marathon would improve your confidence going into your Ironman, for whatever reason, that’s also a good reason to sign up.
But if you do want to run a marathon for any reason, do so during the season prior to or no later than 16 weeks before your Ironman. This will allow you to devote a good proportion of your training hours to running before the swim and bike volume gets substantial and also allows you time to properly recover from the marathon before those big Ironman training weeks.
Alison Freeman is a co-founder of NYX Endurance, a female-owned coaching group based in Boulder, Colorado, and San Diego, California. She is also a USAT Level II-certified and Ironman University-certified coach as well as a multiple iron-distance finisher.