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Keys to Preparing for IM Hawaii, by Karoly Spy

The IM of Hawaii is a mythical and demanding race which is by far the one with the highest density on the world circuit, whether for pros or amateurs. 

When you have the chance to qualify in Hawaii, you have to prepare specifically to try to achieve your best performance there. 

The preparation for this race is special and should not leave anything to chance because you can have the best training in the world, but it will be of no use to you if you have not acclimatized to the humid heat beforehand or if you do not have not prepared your stomach and intestine to ingest a high dose of carbohydrates (90 to 120g/h). These 2 elements (heat & nutrition) are the key points of performance in Hawaii. 

The idea of ​​this article is to provide you with some details on each important component of the preparation for the IM Hawaii so as not to leave the Hawaiian island frustrated with your performance.

1. Let's talk a bit about pacing

Pacing corresponds to the gait strategy that will be the most effective, and will therefore allow the athlete to release the highest mechanical power during the entire event. Abbiss & Laursen reported in 2008 the gait strategy generally used on IM distance.

From this graph, we therefore see that the intensity developed (represented by the evolution of the heart rate) decreases continuously from swimming to running. Related to a test like the IM in Hawaii (of which, it will be recalled, the density per level is maximized), such an observation is likely to be reinforced. In other words, in a pace configuration where the confrontation with other athletes is exacerbated, the athlete often (always?) engages in higher paces, saying to himself: "I'm hanging on to the maximum, this time that go perhaps pass ". Unfortunately, this kind of strategy never works on Ironman with often great suffering during the marathon.

To determine an adequate individual pacing it is necessary to identify before the event the causes of fatigue (on IM distance) which can have a negative consequence on the management of pace. To name a few (Burnley & Jones, 2007):

  • Glycogen depletion
  • Hyperthermia according to environmental conditions
  • Possible dehydration
  • The appearance of muscle damage
  • The decrease in central command (at the nervous level) which reduces the intensity of muscle contraction
  • High levels of neuromuscular fatigue
  • The decline in motivation

We can play on these different elements using a specific approach:

  • Setting an Optimal Tempo which will have been worked on upstream during the preparation with specific sessions.
    • The concept of critical intensity (linear relationship between intensity and time) is an effective approach proven over IM distance. Simply put, the longer the event, the lower the intensity.
    • Various field tests can be used to define the critical power/speed. 
    • The critical intensity can be maintained for about 60', a simple approach can consist in carrying out an effort at maximum intensity for 60' to obtain an approximate value of its power/critical speed.
    • From the knowledge of this data, depending on the profile of the route (flat or uphill), we can model the power that can be maintained without generating fatigue that is harmful to the achievement of the targeted performance on the bike and especially on the marathon.
    • You should not see this notion of Tempo on the bike as an intensity that will allow you to achieve the best performance in this discipline, but rather as the management of your energy reserve that will allow you to approach the marathon in the best possible conditions in order to achieve the best overall performance in each discipline and over the entire Ironman.
    • Bike Power Tempo is unique to each individual in relation to their individual power-time relationship.
    • However, we can highlight an average power that can be maintained on the bike course of an Ironman between 75-80% of critical power.
    •  ⚠️ The average critical power that can be maintained is dependent on the duration of the cycling event, the longer the time, the lower the % of critical power.
    • Real-life example of an athlete preparing for IM Hawaii 2022


Preparing for an Ironman requires long hours of training with a significant volume in each discipline. It is carried out at a sustained intensity over a long period of time. This requires training reflecting this requirement. It's not short high intensity sessions or low training volume that will prepare you to perform on Ironman! 

It's the long sessions with perfect intensity control, to allow an improvement in mitochondrial efficiency, the optimized use of energy sources or even to push back the threshold of tolerance to fatigue, which are important! You have to focus on the process that will lead you to be the most efficient over the Ironman distance. 

Here is the presentation of a 200Km session including 140Km at specific Tempo + 10Km fatigue tolerance work 👇🏻

  • We can see that the power and the HR remained relatively stable on the Tempo part with an average pedaling rate @80 rpm which is a good ratio between force and velocity over the Ironman distance. 
  • On the 10Km Z2 part, we can visualize a good regulation of the SNA with an increase in HR (HRmean +19bpm) and the ability to increase power in a state of pre-fatigue after 160Km.
  • This session allowed a validation of the Tempo both mechanically (power), physiological (little cardiac drift), and perceptual with an RPE of 4-5/10. 

The approach is identical in C34P with long-term work. Example: 29Km including 2Km Tempo + 2Km ZXNUMX 👇🏻

  • We can see a good intensity-HR relationship during the Tempo part. This session indicates good aerobic efficiency with a lower HR in relation to intensity. 
  • On part Z2 one can visualize a marked cardiac drift (HRmean +14bpm) which is proof of a positive adaptive response of the ANS. 
  • The mental aspect is also worked on this type of session in order to strengthen the mental resistance to the effort which makes it possible to endure the maintenance of a target intensity for several hours despite an increase in the level of fatigue.

2. Which nutritional strategy on IM

Energy expenditure over Ironman distance (IM) is very high, around 8500 to 11500 Kcal with an average around 9040 Kcal (Laursen & Rhodes, 2001). The stock of glycogen (storage of carbohydrates in the muscles and the liver) of the human body amounts to approximately 3000 Kcal while the stock of lipids (fats) amounts to 68 kcal (for a 250kg athlete with a 70% body fat). One might think that the stock of lipids is sufficient to cover an Ironman without exogenous energy supply but unfortunately it is not that simple. Indeed, even with a high rate of fat oxidation, the athlete will not be able to meet the energy demand required during an MI only with lipids, he will also have to have an exogenous carbohydrate intake.

The ingestion of exogenous carbohydrates during an MI allows:

  • To preserve the stock of glycogen which is essential because a depletion of glycogen reserves causes muscle fatigue and a decrease in the coupling excitation-muscle contraction
  • To be faster on ultra-endurance events by delaying the onset of fatigue
  • To maintain a high intensity of exercise or a relative intensity over a long period of time
  • Limit muscle damage during exercise and improve post-exercise recovery

The latest scientific advances have shown that a carbohydrate intake of between 90g/h and 120g/h, depending on the athlete's ability to assimilate them without gastric disorders (TG), is an effective nutritional strategy for performance. in endurance events.

You have been warned!

The use of this carbohydrate dosage is only made possible if you opt for a drink containing 2 intestinal carbohydrate transporters, namely SGLT1 for glucose and GLUT5 for fructose. Indeed, the intestines cannot absorb a quantity of carbohydrates >60g/h if there is only one glucose transporter. The ideal composition of the drink will be 2/3 carbohydrates and 1/3 fructose. To assimilate a dosage of between 90 and 120g of carbohydrates/h, you have to train the stomach and the intestine well upstream.

Carbohydrates and lipids are therefore interesting for performing on IM, it is therefore necessary to optimize their use with a cross-training approach aimed at increasing the capacity for oxidation of fats while optimizing the capacity for oxidation of exogenous carbohydrates. A periodized approach to nutrition in training by scheduling sessions with low carbohydrate availability to promote adaptation of fat metabolism and other specific training sessions with high rates of carbohydrate ingestion to train fitness. stomach and intestine to absorb exogenous carbohydrates to reduce TG. 

A new approach to nutritional periodization during training sessions is currently emerging, the benefits seem interesting for improving metabolic flexibility (ability to use carbohydrates and lipids during exercise). This new approach is currently being tested with the group's athletes.

3. Jetlag management

There is a 12-hour time difference between Hawaii and our home country, so you have to prepare for it in advance in order to absorb it so as not to be totally out of sync on the start line, which would have a negative impact on performance. 

Practical recommendations for jet lag converge on the idea of ​​adjusting one's biological clock by 1 hour per day for each hour of lag, suggesting here to regulate one's bedtime and wake up almost 2 weeks before the event. Moreover, since runners in Hawaii rarely travel at the last minute, this strategy must be pursued during the days spent at the competition site. Interventions to promote sleep (relaxation, mild room temperature, hot shower, light meal, milky drink with honey, listening to one's sleep cycle, etc.) such as those to delay it (coffee, light, intense physical exercise, noise, smartphone, etc.) take on their full meaning in this context. Similarly, moderate naps (about twenty minutes) can allow you to cope with the implementation of this time adjustment.

4. Acclimatize to face harsh weather conditions

On average, the ambient temperature in Hawaii rises at this time of year to ~30° with humidity >50% (generating a felt temperature of +5-6°). Consider that this type of thermal environment induces on average a loss of ~2%, ~7% and ~16% for exercise durations of ~6min, ~30min and ~70min, respectively. Imagine the decline in performance for an Ironman in heat if you are not prepared for it…?! Heat acclimatization is one of the keys to performance on the IM in Hawaii, it reduces thermal stress during exercise, potentially improving performance.

It could not be easier ! Try three weeks before the competition to carry out your sessions at low intensity in a room heated to a temperature of 30°C, and this for > 60min at a rate of 3 times / week. If you go gradually and stay tuned to your feelings (no overload!), then you will teach your body to better tolerate (mentally!) and evacuate (physiologically!) the heat it stores during exercise. . After 10-12 sessions (without too much gap between them), you will see for yourself how effective this heat acclimatization strategy can be...

With the group, we use an alternative approach by taking post-exercise hot baths to better withstand the humid heat. The advantage of the post-exercise hot bath being that it does not interfere with training and is easy to integrate into the preparation. To achieve complete heat acclimatization, it is important to raise both core body temperature and skin temperature. Taking a hot post-session bath allows for this combined rise in core body temperature and skin temperature. The heat cannot dissipate in the moist heat of the bath, which improves the specific mechanisms for acclimatizing to the moist heat.

5. The Sharpening Approach

Sharpening is a strategy of manipulating the volume and intensity of the training load to reduce training fatigue without losing hard-won adaptations.

The reduction in the training load initiated by the sharpening phase will reinforce physiological adaptation at the molecular and cellular level, but also at the psychological level.

The various scientific studies on the subject recommend sharpening times between 4 and 28 days (Mujika & al, 1996; Mujika & al, 2002) including a gradual decrease in training volume, maintenance of the frequency of sessions and a gradual reduction in intensity.

But sharpening is above all a personal matter since each body reacts differently. You have to listen to the athlete and know his own reactions in order to individualize this very complex period. 

Indeed, for some athletes, you have to be careful to maintain a certain level of load to reach the Top on D-Day, while for others, you have to drastically reduce the training load in the last week so that they can mentally recharge. / physically. Sharpening approach is also strongly correlated to the athlete's average training load volume over the last few months. When the athlete is used to training 2-3x/day with a high volume, the sharpening will be shorter than an athlete with a lower training volume. The key element of the sharpening period will be above all a precise control of the training intensities in the last 7 days and a follow-up of the regulation of his nervous system (ANS) by controlling the evolution of his HRV and his wellness. . 

You should know that the psychological aspect is an important element to take into consideration, the athlete must feel good in the last days before the goal to be confident in his abilities. Saw & al (2015) analyzed 56 studies on the subject of training load monitoring. It emerges that the monitoring of the well-being (wellness) of the athlete is an essential element to guide the training and the sharpening phase. 

6. Conclusion

The various points mentioned in this article (pacing, nutritional strategy, Jet-Lag management, heat acclimatization and sharpening phase) should help the athlete to achieve his best performance on the IM of Hawaii but also on the races with an identical format. Other elements have not been mentioned but are important to consider: 

  • HRV Guided Training
  • Biological monitoring with hemoglobin assay
  • Hyper-hydration
  • Aerodynamic optimization
  • Reduction of endogenous heat


This article was written by Karoly Spy, trainer specializing in endurance sports.
  • Founder of KS-Training in 2007 to support athletes in their performance project
  • Founder of the GUTAÏ Training application (2016-2021)
  • Coach trainer
  • Technical Advisor for the Franche Comté Triathlon League (2005-2007) and for the Provence Alpes de Triathlon League (2007-2012)
  • Coach in athletics club (Vitrolles, OM Athlé, SCO) and in Triathlon club

Find his website: 

Discover the original article  HERE.

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