What does it take to finish an Ironman?

A bit of a departure this week from my regular focus on high performance athletics to discuss the level of fitness required to complete an Ironman race in under 17hours.

Before I whip out the scalpel and start dissecting, a couple of quick observations on the psychology of the Ironman finish…

Having the chance to coach some first time IMers has been an interesting experience. Not so much from the physical side of things, as I point out below, the physical equation for an Ironman finish is quite simple – get the athlete fit, strong, and teach appropriate pacing. But the psychology of an athlete’s first attack on the Ironman distance is a thing of pure beauty.

In my experience, a first time Ironman has a perspective that often fades as the athlete morphs into a ‘mid-packer’. The magnitude of an Ironman finish is not lost on the first timer and the accompanying fear offers real, pure, motivation.

The athlete pictured above, Louie Bonpua exemplified ‘pure motivation’ better than anyone I can think of. For more on Louie, click here…

I know, thinking back to my own first marathon, the daunting task that lay ahead and the accompanying fear of ‘the wall’, ‘the bonk’, ‘the bear on the back’, motivated me to train seriously – 45-50 miles a week for a good 3 months prior. Right or wrong, after completing several of these, along with some Ironman races, century bike rides etc, I think I have tended to lose that outsiders perspective on the significance of running a marathon and the respect that the distance deserves. The same thing often happens as an Ironman athlete has a finish or 2 under their belt.

Make no mistake, the Ironman offers no mercy for those who have tread those roads before. She is and will always be a distance that demands the utmost respect, to finish an Ironman on any day is a significant accomplishment, one which is often forgotten by the experienced IMer until they experience the joy of crossing that line one more time.

So, let’s delve in to what purely ‘crossing the line’ entails in a little more depth….

Endurance

Of course, an Ironman finish requires substantial endurance. But what, physiologically, does this mean?

In events over approximately 90 minutes in duration, the #1 thing that ultimately will force the athlete to slow down (or stop!) is most likely to be running low on glycogen. Therefore, any athlete who takes on the task of Ironman is going to want to maximize their glycogen stores.

This is an interesting adaptation because, given the right (glycogen depleting) exercise, athletes can almost double their glycogen stores within 10 weeks of specific, intense training (Greiwe et al. 1999). Thereafter, very little change is expected.

In specific numbers, an average sized male athlete may begin training with glycogen stores of 1650kcal and after 10 weeks of training may be up to 3300kcal. In other words, time to exhaustion in glycogen depleting activity roughly doubles. Obviously this is a key adaptation for the Ironman athlete

Metabolically, the other 2 key sources of energy for our Ironman athlete are their fat stores and exogenous glucose, i.e. sports drinks, gels, bars etc taken during the race. Maximizing the energy contribution from the first is a long term training adaptation. However, maximizing contribution of the second is purely a case of being out there long enough to digest the carbohydrate. This is where the back of the packer picks up a significant advantage.

While it may take roughly the same energy to cover 140.6 miles irrespective of the speed you do it, those who space out their effort over a longer time are able to take in and digest more exogenous carbohydrate along the way. Therefore, while a front of the pack guy may only have sufficient time to digest and use an extra 1800 calories worth of sports nutrition, a ‘back of the packer’ who is out there for 17hrs may get an extra 3800 calories from outside sources!!

OK, so assuming we have maximized our energy stores to 3300 cals and we’re out there long enough to get another 3800 cals from food, how fit does the athlete have to be to use this 7000 cals of energy to get from A to B in less than 17hrs?

Fitness

So, in pace/power terms what are the requirements for a 17hr finish?

Assuming an ~ 8.5hr bike and ~6.5hr marathon, an 80kg athlete will be putting out anything from ~80W on a flat course to ~120W on a hilly course. Additionally, they will be walk/jogging at ~4 miles per hour.

In fitness terms, sounds pretty tame, eh? But keep in mind that for most athletes, this ‘fuel economy mode’ of 400 cals of carbohydrate per hour is (based on our lab data) only going to enable them to work at 50-55% of their max aerobic power.
So, keeping in mind that the athlete will only be able to hold ~55% of max aerobic pace/power over this distance, in my opinion, an athlete hoping to break 17hrs, in addition to the requisite endurance training needs to be fit enough to have VO2max numbers of ~160-240W on the bike and 8 miles/hr on the run. Based on ‘normal’ economy data, this translates to a VO2max of ~30ml/kg for a flat course to ~40ml/kg for a hilly course.

I’ve provided a couple of charts with VO2max norms for male and female athletes below to put these numbers in perspective for different age groups. My suggested ‘tough course’ IM requirements are in red, with ‘flat course’ IM requirements in yellow.





As indicated, any older athlete, particularly any older female athlete that finishes an Ironman under 17hrs is VERY FIT! Even an older guy of 40+, who finishes an Ironman under 17hrs is likely fitter than 98% of 40 y.o guys across the country! This puts ‘Iron fitness’ into true perspective.

The magnitude of a tough Ironman finish for an older athlete is borne out in the results. In Lake Placid in 2009, for instance, 1 out of every 5 guys in the 60+ age groups DNFed or failed to finish within the cut-off. For the 20-29 guys, only 1 in 23 failed to make it. For the women, a finish is even more impressive. Of the 5 females who started in the 60+ age groups, only 1 was able to complete the course under 17hrs!

These numbers only serve to make me respect the ‘Iron-vets’, even more than I already do. There are some supremely fit older guys that I’ve had the pleasure to cross paths with over the past 10 years or so of IM training.

In a world of Kona obsession, hopefully these numbers also serve as a reminder to all athletes, even the young ones, that finishing an Ironman puts you in the crème de la crème of fitness when compared to the rest of the population. Simply put, when it comes to fitness, finishing an Ironman or multiple Ironmans is a very worthy goal.

Anyhow, back to the numbers….

For those without access to lab testing, the VO2 numbers that I’ve mentioned correspond with a 5K run fitness of sub 35min 5K (for flat IM) to sub 25min 5K (for hilly IM) and FTP numbers of 1.75W/kg (flat) to 2.6W/kg (hilly).

These numbers offer the first time athlete looking for a sub 17 finish a good ‘reality check’ on their basic fitness prior to beginning the more specific preparation workouts designed to acquire the necessary endurance for their IM.

Additionally, for the more experienced athlete, by knowing where the athlete’s basic fitness is, more appropriate pacing goals can be better set for the specific endurance workouts going into an Ironman race preparation phase. This is a very practical way of applying a reverse periodization approach for Ironman athletes. But that’s the topic for another blog…

Train Smart!

AC