Xtri is pleased to introduce The Corner. This is a new weekly column on Xtri that is an extension of Endurance Corner. The Corner will feature articles from Gordo Byrn, Alan Couzens, Justin Daerr and other members of the Endurance Corner team that discuss training, nutrition, physiology and all topics important to the multisport athlete.


As exercise physiologist for the Endurance Corner team, I have been in a unique (and fortunate) position to perform or analyze tests for over 140 athletes over the past 2 years, ranging from sub 8:40 to 15:00+ Ironfolks. My perspective is especially unique because the vast majority of these athletes have been, specifically, of the Iron persuasion.

Recently, I took the time to compile this data in a database so that we can deduce norms and, by comparative means, identify specific indicators of strengths and weaknesses for future athletes who will come through our lab. I thought that the some of the implications arising from this data may be of particular interest to you, the X-Tri readers. The data offers some insight into common questions that keep cropping up on the various internet forums. Questions like;

1. How important is VO2max to your performance as an Ironman athlete?

2. Does functional threshold power correlate well with Ironman performance?

3. Is "fat burning" an important physiological quality for the Ironman athlete?

I took the 84 tests from the database from which we have good data on all of the above from specific Ironman athletes to offer some educated opinions on the above.

VO2max

It has been said that, in the world of endurance athletics, while a high VO2max may not make you prom king or queen, it does give you a ticket to the dance ļ In an absolute sense, the same is true of Ironman.

VO2max is made up of 2 basic components;

1. The amount of oxygen your blood can pump (Cardiac Output)

2. The amount of oxygen your muscles can take up (a-VO2 difference)

Each component is of equal importance. However the Cardiac component is somewhat limited. Just as some folks are born with big ears or a big nose, others are born with a big heart (and some other factors that help with O2 delivery). That's just the way it is.

The good news is that VO2max as a whole isn¡¦t as important in Ironman as it is in some of the single sports. Based on our data (see below), VO2max only explains 35% of the difference in Ironman performances, with an 8:30 Ironman only "requiring" a trained VO2max of ~4.6L/min. To put this in perspective, ~20% of the population have VO2max values that are within reach of this in a trained state. A 10:00 IM requires only ~4.3L/min. Or, in other terms, ~50% of the population are within reach of a Kona slot, providing they put in the work!

So, in practical terms, what is "the work" to improve VO2max? Basically setting up a training program that addresses maximal aerobic fitness in all fiber types (a general, multi-speed program), while taking care to avoid work that leads to high levels of lactate accumulation. This means a lot of base work, some sub-threshold work and a small amount of speed work over short distances.

So, if VO2max only explains 1/3 of Ironman performance, what physiological factors make up the balance?

Body Mass

Despite our athletic pre-occupation with weight, body mass index represented only 4% of the sample variance in Ironman performance. For what it's worth, the mean value of our top performing athletes (9:00) was 22.75, or ~163lbs for a 6ft male - not ectomorphic by any means!!

Functional Threshold

If Functional Threshold is expressed as a relative measure, i.e. absolute VO2max is taken out of the equation, differences in Functional Threshold Power represent 12% of the differences in Ironman performance within our sample. This is definitely a significant chunk of the pie (of similar proportion to improved fat oxidation ¡V see below).

However, in practical terms, it needs to be remembered that the power that you are able to hold at functional threshold is a composite of the amount of lactate produced and consumed by all fiber types up to the point at which lactate production begins to exceed it¡¦s removal. In other words, improving one's functional threshold is about more than tough 1hr trainer sessions. Tempo work, long base rides and just plain old volume all play a part.

Fat Oxidation

Despite the controversy over the link between Ironman performance and fat oxidation, at least in our sample, fat oxidation contributed to 9% of the difference in Ironman performance between our athletes. Unlike Functional Threshold, where those with a high Functional Threshold tended to also have a relatively high VO2max, there was less of a link between VO2max and fat oxidation. In other words, certain athletes with relatively low VO2max values made up some of the difference by improving their ability to generate energy from fat burning!

More good news: In addition to all of the general fitness factors mentioned above, high levels of fat burning are strongly linked to the athlete's diet. In other words, those folks who are committed to eating right have the potential to beat 10% of the field that may put up better aerobic numbers purely by saying no to the twinkies!!

Other stuff:

Overall, the physiological factors explained about 60% of the differences in performance for the Ironman athletes that we tested. While I don't have the numbers to prove it, I would suggest that, as far as endurance sports go, Ironman is one of the least physiologically determined of all the endurance sports. I would guess that if we did a similar analysis on say 5K run performance that differences in physiology would explain most of the differences in performance.

Put another way, the Ironman athlete has a lot of alternative avenues that they can explore to make up for physiological shortcomings:

Course selection: Probably the easiest way to improve your IM PR is to simply choose a flatter, less windy course. As Forest Gump says, "That's about all I have to say about that."

Aerodynamics: I have seen differences in frontal area for Ironman bike positions of athletes of similar size in the range of 0.4-0.55m2. This represents a difference of ~40W for a 5:30 bike split! For comparative purposes, a similar physiological improvement in aerobic capacity will likely take 2-4 years of training for the typical athlete!!

Execution/Nutrition: We have all seen the effects of pro triathletes who screw up their pacing or nutritional plans. No matter your physiological capacity, if you bonk, expect half of the field to overtake you. At each Ironman race there are those seasoned athletes who, through perfect execution of their pacing and nutritional plan, outperform many physiologically "fitter" athletes.

Hopefully this article has helped to shine some light on the mystery that is Ironman racing. For further reading on some of the topics mentioned above, check out Alan's blog on the endurance corner website: www.endurancecorner.com/ac_blog.

Train smart,
AC


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Alan Couzens, MS (Sports Science), CSCS, PES, is a coach and exercise physiologist who helps athletes over at www.EnduranceCorner.com. He has a passion for performance and has been coaching endurance athletes since 1993.