Asker on the run course in Kona

Dr Brent Ruby Ironman Triathlete and researcher

Carb intake
There is no sport where nutrition plays a more crucial role than Ironman. Nutrition can not only be the difference between finishing first or second, it can be the difference between finishing and not finishing. And although this may seem a bit dramatic, in extreme conditions, it can be the difference between living or dying.

The total energy expenditure of an Ironman will range from approximately 8,000-11,000 kcal. A colleague and good friend of mine Dr Bent Ruby, director of the human performance lab at the at the The University of Montana-Missoula used the very expensive doubly labeled water technique on himself to accurately quantify the energy expenditure during his Ironman Hawaii race in 2006. He finished in just over 10 hours. In an abstract presented at the American College of Sports Meeting in Indianapolis in 2008 it was reported that his energy expenditure was 9,290 kcal.

It is impossible to consume that much energy during an Ironman and stay in energy balance. Studies in cyclists have shown that athletes often choose to ingest as little as 25 g CHO per hour or 100 kcal/h. Even when the carbohydrate intake is pushed to high levels it appears that the maximal rate the muscle can use this carbohydrate is approximately 1 g/min (60 g/hour, 240 kcal/h). This really is a small amount of energy and even when you would ingest the large amounts every hour, the total energy provision via food during the race would only be 2,400 kcal for a 10h Ironman or 3,600 kcal for a 15h Ironman. So an Ironman will always be performed in negeative energy balance but this is ok, because the days after there will be plenty of time to catch up on the calories.

Carb intake
The science is pretty convincing on the benefits of carbohydrate (CHO) intake during prolonged exercise. The science is also pretty convincing that severe dehydration reduces performance and can even be health treatening.

In terms of fueling, the trick is to…

• take in enough CHO to provide an additional fuel source to the working skeletal muscles
• not to take in too much to create major upper or lower intestinal distress (certainly no number 2s!)
• maintain blood glucose to limit unnecessary weeping and gnashing of teeth (cognitive decay) on the race course
• be willing to adjust intake under a variety of weather conditions. 

In terms of hydration the goals is to

• minimise weight loss. Some weigt loss is accapetable as you will lose fat and carbohydrate (plus associated water that was stored with the carbs) but weight loss of more than 2 kg could defnitely affect performance.
• Optimise hydration by adding some sodium and some carbohydrate

In an ideal world all of the carbohydrate ingested get immediately utilised by the muscle (oxidized). The amount of carbohydrate oxidized from a drink/gel/bar depends on:

• How much carbohydrate you take on board
• The source or sources of CHO consumed (for example glucose, sucrose, maltodextrions, fructose)
• Possibly the form in which the carbs are consumed: solid or liquid or semi (gels)
• The weather (lower tolerance in hot weather)
• Intestinal/stomach training (the “are you used to it” factor)

Type and amount of carbohydrate

There appears to be a growing amount of evidence that one source of CHO alone is less appropriate than multiple sources. Typically, maltodextrin (a relatively flavorless complex CHO – know to the stomach as multiple glucose molecules put together but easily broken apart starting in the mouth and completely in the stomach), is a “quality” CHO.  However, other CHO sources (fructose, sucrose) have gotten a bad reputation and are thought of as cheap CHO sources.  However, our studies have clearly demonstrated that you can increase the rate of exogenous CHO oxidation if you consume a combination of glucose (or maltodextrin) plus fructose.  The approximate ratio is 2 parts glucose sources and 1 part fructose.  The reason for this is that glucose and fructose appear to use two different transporters to gain access to the blood (absorbed in the small intestine).  By taking advantage of these two transporters, more of the CHO you consume will be available and eventually oxidized by the skeletal muscle. Ten years of study in our lab has shown that mixtures of glucose and fructose, maltodextrins and fructose, or glucose, sucrose and fructose can increase oxidation rates up to 1.75 g/min!!  (75% more than what was previously considered as “maximal”!).

In addition to this we have also found that fluid delivery with these drinks is improved by a similar extent and recently we found that performance was more improved with these mixtures compared with a traditional sports drink. Another huge advantage of these drinks is that gastro-intestinal problems are reduced. This is not unexpected because if more of the ingested carbohydrate is oxidized it is not sitting in the stomach and intestine to cause problems!
It must be noted that such high levels of energy delivery can only be achieved if a very aggressive feeding regimen is adopted. You need to take on board very large amounts of carbohydrate!! And the common sense message is “don’t try this at home!”. Well actually, you should probably try it at home but “Don’t try it in Hawaii!”.

It is relatively easy to make these drinks yourself. The ingredients are simple: maltodextrins, fructose, salt and water! However, there are also a few products available that have adopted this composition! One of them (PowerBar) happen to be handed out at the feed stations in Hawaii. Both the powerbar gels and bars contain glucose and fructose in a 2:1 ratio. PowerBar have called the carbohydrate mix C2max. Read more about the science behind C2max on their web site.  

What is available on the course?

Because it is impossible to carry all necessary calories on the bike (and run), the first step in preparing a nutrition plan is always to find out what is available on the course. In Kona this will be:

• Water
• Gatorade endurance formula
• Cola
• Powerbar gel
• Powerbar bars
• Bananas
• And other foods which would not form a major part of my nutrition plan

The next step is to analyse the composition of these foods. The composition of the gels a 500 ml bottle of Gatorade Endurance, one gel or one bar are listed below:

The drink I have trained with is the Powerbar Endurance drink, so I will take 2 x 750 ml bottles of that drink with me on the bike:

Then as a next step you will need to know the aims: in my case I will be aiming for a carbohydrate intake of up to 90 grams per hour whilst minimizing fluid losses. From the hours I spend in an environmental chamber I know that my sweat rate will be over 1 liter per hour and therefore I will plan to drink 1 liter every hour. From experience I know that this is a large volume but I should be able to do this for at least the first 6 hours of the race.

So on the bike I will attempt to use the following. It is likley that I will not be able to consume all of it but depending on how I tolerate it all, I will try to get as much in me of this as possible on the bike:

I will put all 16 gels into one drinks bottle and fill this up with water (This is something I have done in the last few Ironman races). I will keep sipping from the bottle with the gels and rinse my mouth with water afterwards.

This, in simple terms translates into: 1 bottle every half hour and 2-3 gels per hour by taking small sips from the gel bottle. In previous races where I tried to rely on gels and drinks only, I got a rather empty feeling on the run and therefore I will try to incorporate a bit more solid food. For me banana seems to be the food I tolerate best but I am also taking a PowerBar as that is what I have done in the past. In the first couple of hours of the bike I can usually still eat.

On the run I would go to 2 gels per hour plus water. Then usually towards the end the well planned strategy goes out of the window and I will have to take whatever I can tolerate (coke, water, banana).