Carbohydrate Loading for Ironman Athletes.

Alan Couzens, MS (Sports Science)

May 30, 2014

In my previous post, I weighed in a little on the LCHF debate. As I outlined in the post, valid arguments can certainly be made for moderating the carbohydrate intake during the bulk of the training phase for most athletes. However, as we move from training to taper, different considerations emerge that will have impact on the optimal pre-race diet for the endurance athlete.

Studies have consistently shown a strong relationship between starting CHO stores and time to fatigue at submaximal intensities. For example, Balsom et al., (1999) found a 50% decrease in time to fatigue when subjects began an exercise test with a 50% reduction in glycogen stores. This almost linear relationship between starting glycogen stores and time to fatigue has been observed in numerous studies. Therefore, a key objective heading into your A-Race is to maximize this adaptation. The good news is that it doesn’t take a lot of time or effort to maximize this adaptation. However, it does require doing things a little bit differently to your normal training and nutritional routine and perhaps a little different to a normal taper routine for a shorter distance athlete.

Ironman legend, Torbjorn Sindballe comments on some of the differences here...

“ If I only did shorter sessions for the few weeks leading into a race, I often felt super fresh but lost my momentum after hour three or four in the race. To combat this, I implemented a big rest phase to reduce fatigue several weeks before a big race and then did a series of more normal training sessions in the weeks leading up to the race”

What he’s referring to is a very real physiological phenomenon of metabolic detraining. While, most physiological adaptations can be sustained on relatively minimal volume for 3-4 weeks, if an athlete does not ‘challenge’ the ability to hold on to larger than normal glycogen stores, it is an adaptation that is lost rather quickly. A typical rate of ‘metabolic detraining’ is shown in the chart below (data from Casey et al., 1995).

In the absence of sufficient stimuli, the body will lose 10% of its glycogen stores within 2 weeks (more if the lack of long rides extends into other weeks!) & you will lose 10% or more from your time to fatigue! For this reason, including regular moderately long sessions, even relatively close to an Ironman, is a very worthwhile strategy for the serious Ironman athlete, as suggested by Torbjorn. However, it is not just the shift in race week training that will enable you to elevate your glycogen levels to new highs. The training must be accompanied by a similarly appropriate nutritional strategy.

To increase your body’s receptiveness to storing glycogen, demands a little bit of a departure from a normal taper routine in both training and nutrition. Here is what I suggest for the long course athlete…

5 days out (Tuesday) – Do a moderate length/intensity session with minimal CHO intake designed to take your CHO stores relatively low. Something in the vicinity of 4hrs/200TSS with some race pace efforts on ‘water only’ or very light CHO. Tuesday following the session – big CHO! This should be an ~600-800g day accompanied by a good amount of fluid & normal protein/fat. Have your own mid-week pasta party!
3-4 days out (Wednesday/Thursday) – Decrease overall caloric content but keep CHO proportion high (70-80% - 400-600g/day depending on the size of the athlete).

1-2 days out (Friday/Saturday) – Begin to move towards more easily digestable CHO. Be conscious of not taking in foods which will be slowly digested (fats/fiber etc). Typical transit times for fats are ~72hrs. This number can be greater under periods of high stress! While, you don’t want to omit fat entirely, having a large amount of undigested fat in the system has the potential to both slow digestion of the important carbohydrates and lead to gastric distress so begin to minimize this 72hrs out. Additionally, some athletes find benefit in minimizing gluten and dairy during this period as these are 2 of the most common digestive ‘irritants’ among athletes.

Race morning – Take the easily digestable to the extreme. Try and get 80-100g of CHO for every hour that you are up prior to the race with a good chunk coming from liquid or semi-solid forms. Ideally this will be 3-4hrs so 300-400g of CHO total, progressively tapering down towards race start. An example might be…

Wake up 3-4 hours prior to race start...
Hour 4-3: 3 Ensures (100g) +Ripe Banana (27g) = 127
Hour 3-2: 2 Ensures (66g) + Ripe Banana (27g) = 93
Hour 1-2: 1 Ensure (33g) + 0.5 banana = 50
Hour 0-1: 0.5 Banana in transition. (13g) = 13
----
~300g

This final ‘meal’ on race morning can really be thought of as your first race nutrition. We are looking to provide the body with calories that can begin to be digested in the easiest part of the race day (before you’re even racing :-) This will help to get you through the swim and the early bike. Just as it is important that it is easily digested and you're not going to be carting it around all day, it's equally important that we don’t want something that is going to hit your blood stream before the gun goes off(!), so stay away from gels and the like and be sure that whatever you eat has a little bit of fat and protein to slow digestion. For folks who can tolerate solids, a bagel or 2 with a little bit of nut butter is another suitable alternative.

Also, while we set it up with an aim to be easily digested, pace these early phases with the realization that in addition to race energy you will be using some energy in the early race for digestion. If you’re able to get this last meal digested well in the early period of the race, it will come back to benefit you ten fold when energy stores are running low & digestion may be more compromised late in the day.

Whichever nutritional option that you go with, be sure to test it before race day. Ideally in one or more of your simulation workouts in that final race preparation phase.

Eat smart!

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