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Science Geek Tuesday! by Tammy

Having had my own nutritional setbacks in shorter-distance triathlons got me wondering about Ironman. How can one possible intake the amount of food required to fuel such an undertaking? The answer: they can’t.

According to research by Kimber et al, kcals burned during an Ironman event are 10,036 for males, and 8,570 for females (when you adjust for fat-free mass, these numbers are comparable, indicating both males and females expend the same amount of energy in an Ironman event). Based on research by Hawely et al, the maximum amount of CHO (carbohydrate) that can be oxidized in skeletal muscle is 1 g * kg -1 * h-1 (1 gram per kilogram of body wt per hour). This results in a mean energy deficit of -5973 and -5123 kcals for males and females respectively. What does all this mean? It means that if you compete in an Ironman event, 59% of your energy needs will have to come from endogenous (already in the body) fuel stores. This really drives home the importance of maximizing your body’s fuel stores prior to your event, but also stresses the extreme hit your body will undergo in this event, and the need to focus on recovery to avoid injury and/or illness following the event.

This research was conducted using participants of the 1997 Ironman New Zealand. 8 females and 10 males participated in this study, so it was a small sample, but the findings are backed up by other research from various trials. One of the focuses of this study was to identify gender differences in energy intake vs. energy expenditure. Interestingly enough, they found that females who took in more CHO, had longer finish times, whereas males who took in more CHO, had shorter finish times. One indication of this finding is that the difficulty of digesting high amounts of CHO had a greater impact on the female athletes. There is also an indication that females, with higher fat mass, are better able to utilize endogenous lipid stores, therefore having a competitive edge over their male counterparts, and not requiring the same high CHO intake at the end of the event (the females with the shorter finish times ingested less CHO in the run segment). This information stresses the importance of finding what works for you as an individual. This means, of course, training like you race. Don’t rely completely on input from coaches and/or mentors. Use their advice as a starting point, put it into action, and adjust according to your own results.

And I’ll leave you with these last interesting facts. 94% of energy consumption by these athletes was in the form of CHO. 73% of energy consumption occurred during the cycling segment. While we all know the CHO is the main substrate in short, high intensity activity, these findings surprised me for an Ironman competition, which should be at a much lower intensity. Good to know… stick with the carbs! As for the majority of consumption happening on the bike, that makes perfect sense. You can’t eat while swimming, unless a random piece of seaweed finds its way into your mouth; and eating while running… not so easy on the GI tract. I found during my Olympic that I didn’t want to get out of my groove to grab my gel bottle on the cycling segment, so didn’t get as many calories in as I could/should have. I paid for this on the run. Luckily I made it to the finish without eating any of my competitors, but it was a close call! ;)

Until next time, Stay Geeky!
Tammy
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Refs:

Kimber et al., Energy Balance During an Ironman Triathlon in Male and Female Triathletes. Int. J. of Sport Nutr and Ex Metab, 2002, 12, 47-62

Hawley et al., Oxdation of carbohydrate ingesting during porlonged endurance exercise. Sports Med. 14:27-42, 1992.

Would you like to read more from Tammy? You can find her at No Try!