A triathlon consists of three disciplines, each with its own specific challenges and demands. In addition, every athlete is unique and has individual strengths and weaknesses. For most people, running a standalone marathon already seems nearly impossible. For the triathlon community, however, it is “only” the final segment of an Ironman. In this article, we will outline the differences and specific characteristics of a standalone marathon compared to the marathon at the end of an Ironman. We will also provide guidance on how to approach the Ironman marathon under the best possible conditions.
As a brief historical anecdote, the marathon discipline traces its roots back to the Greek legend of the soldier Pheidippides, who ran from Marathon to Athens in 490 BC to announce the victory over the Persians to the Assembly. In 1896, with the revival of the modern Olympic Games organized by Baron Pierre de Coubertin, the marathon was included among the original events. The distance was officially standardized at 42.195 km in 1921 by the International Amateur Athletic Federation.
A marathon is an event that challenges the biological functions of its participants. Physiological processes constantly take place to counteract the fatigue induced by exercise. Preparing for a marathon (whether standalone or as part of an Ironman) requires the body to undergo biological adaptations. In this chapter, we will describe the key determinants and limiting factors of performance in a standalone marathon and expand on them to address the specific demands of an Ironman marathon.
Physiological Components
To date, three physiological components are considered key determinants of performance: VO₂max, speed at the anaerobic threshold, and running economy.
Other limiting factors have also been identified, such as nutrition, climate, motivation, and mental endurance, to name just a few. While spending sufficient time training is crucial, it is unrealistic to expect to reach one’s goals without, for example, adopting an appropriate nutritional strategy. Therefore, these aspects will also be addressed in this chapter.
VO₂max
VO₂max is defined as the maximal capacity of an individual to consume oxygen, transport it to the working muscles, and extract it to produce energy. Since we run at a percentage of our maximal oxygen uptake, it is easy to understand that the higher the VO₂max, the greater the “tank capacity.” In practical terms, it is easier to run at 14 km/h if your speed at VO₂max is 22 km/h than if it is only 17 km/h.
In both a standalone marathon and an Ironman marathon, a higher VO₂max increases the speed reserve and makes it easier to sustain a lower race pace. However, because the running speed during an Ironman marathon is lower than in a standalone marathon, dedicating extensive training time solely to maximizing VO₂max—rather than optimizing speed at the anaerobic threshold—may be questionable.
Speed at the Anaerobic Threshold
Speed at the anaerobic threshold strongly influences endurance performance in a marathon. The anaerobic threshold represents the transition point between aerobic and anaerobic energy systems. The aerobic system requires oxygen and energy substrates (carbohydrates and/or fats) to produce ATP, the molecules responsible for converting biochemical energy into mechanical energy. When exercise intensity becomes too high, the anaerobic system is increasingly engaged, leading to lactate ion production. These lactate ions acidify the internal environment; if buffering capacity cannot compensate, maintaining that intensity becomes impossible.
Carbohydrates allow athletes to sustain a higher percentage of their VO₂max. However, they provide less total energy per unit than fatty acids. Motor efficiency and fatigue resistance are trainable and enable biological, biomechanical, and mental adaptations at the anaerobic threshold. In a standalone marathon, athletes start in a relatively fresh state. In contrast, the Ironman marathon begins after many hours of accumulated pre-fatigue.
Running Economy
Running economy can be defined as an individual’s ability to move efficiently from an energetic standpoint. More specifically, it refers to oxygen consumption at a given running speed. This component is directly related to the biomechanical and energetic efficiency of one’s movement pattern. It is particularly improved through years of consistent training and high training volume. However, running economy is also affected by preceding activities. Pure runners are generally more efficient than triathletes, who must divide their training time among three disciplines.
“Completing a standalone marathon as part of an Ironman preparation is of limited value—except perhaps for boosting self-confidence—unless you run it at your intended Ironman marathon pace.”
Nutrition and Hydration: Adopt a Strategy!
Nutrition and hydration are critical in a marathon. A standalone marathon lasts between 2 and 6 hours, yet carbohydrate stores can be depleted within just 90 minutes at 75% of VO₂max. A body weight loss of 2% due to dehydration can reduce performance by about 20%. In a standalone marathon, fueling begins before race day and is adjusted during the event. In an Ironman marathon, however, fatigue and energy depletion are already present at the start of the run.
Weather and Climate
Temperature and humidity significantly affect pacing. A French study by El Helou et al. (2012) involving 1.8 million runners showed that optimal marathon temperature is between 1 and 9 °C, and performance decreases by about 3% for every 0.5 °C deviation. Too cold risks hypothermia; too hot impairs performance due to accumulated metabolic heat. During energy production, oxidation generates heat, increasing core temperature. The body regulates this primarily through sweating. Triathlon is typically a summer sport, and Ironman marathons rarely occur in ideal cool conditions. Moreover, athletes begin the marathon after 3.8 km of swimming and 180 km of cycling—already thermally stressed.
Mental Aspects
Intrinsic motivation—pursuing a personal goal—is strongly linked to performance, while external validation is often associated with poorer outcomes.
Mental endurance is trainable. While the Ironman requires longer discomfort, a standalone marathon often involves higher pain intensity because it is raced closer to physiological limits.
How to Approach the Ironman Marathon
Most athletes aim to finish rather than win, yet fatigue perception is similar across levels.
“The body and mind must be trained to endure discomfort for many hours. Brick sessions and preparatory races are essential.”
As mentioned above, training is the key to success. Proper organization and therefore planning are essential. An Ironman marathon is not approached in the same way as a standalone marathon. The specific demands of an Ironman must be taken into account. In this context, completing a standalone marathon as part of Ironman preparation is of limited interest – except perhaps for self-confidence – unless you run it at your planned Ironman marathon pace.
In that case, it serves as a valuable rehearsal to test yourself under real conditions. As discussed earlier, race paces differ, meaning that adaptations would otherwise occur at speeds that are not specific to an Ironman. In an Ironman marathon, you begin the final discipline more or less depleted of glycogen stores, with already heavily fatigued muscles and central fatigue also contributing to reduced performance.
Taking these specific demands into account, both body and mind must be trained to endure discomfort for many hours. Brick sessions and/or preparatory races are essential. It is also clear that having a high VO₂max will enhance performance in an Ironman marathon. However, race speeds across the three disciplines are so far below VO₂max speeds that this key performance factor is relatively less specifically trained among elite athletes.
Take the example of two Norwegian long-distance elite athletes, Gustav Iden and Kristian Blummenfelt. Both train for many hours, but comparatively little time is devoted to VO₂max work (which they call “X-Element”) compared to anaerobic threshold training. They focus their efforts on the speeds they can sustain during 70.3 and Ironman races and ensure they are highly efficient at those intensities. They make extensive use of lactate analyzers and adjust their training according to changes in lactate levels at target intensity.
Running economy is improved mainly in two ways:
- Working on long repetitions at race-specific target intensity. For example, if the Ironman marathon course includes many climbs, they perform hill work at race pace.
- Running at low intensities for long durations (more than two hours) to prepare physically and mentally for the sensations experienced in long-distance events.
Regarding climate, it has repeatedly been shown that training in the heat improves heat adaptation (see our feature in issue 215), and not only that. Studies show that heat training also enhances performance in cold conditions. To strengthen mental resilience, it is advisable to train in all types of weather. If you avoid training in heat, cold, rain, or snow out of laziness, chances are you will not perform well under those conditions on race day. The Body Core Comp core temperature sensor is a valuable asset for optimizing race strategy, whether in terms of nutrition, thermoregulation, or pacing decisions.
Nutrition during an Ironman marathon differs greatly from that of a standalone marathon. When I read Gabrielle Collison’s book interviewing British marathon stars from the glorious 1980s, many reported not drinking a single drop of water during an entire marathon. That is inconceivable in an Ironman. With heat and gastrointestinal limitations, it is already difficult to limit body weight loss due to dehydration. During an Ironman, proper fueling is essential. Ideally, carbohydrate loading should begin three days before the race, followed by the intake of both simple and complex carbohydrates during the cycling segment to compensate for losses incurred during swimming and cycling.
Finally, there are ways to improve mental performance in a marathon. The most important thing is to know why you committed to this event. It may be to qualify for a world championship, raise funds for charity, honor a loved one, or prove to yourself what you are capable of. Repeat the names of those you love—and keep moving forward, always forward.
The Ironman marathon may seem like an impregnable fortress. However, the distance should not be mystified. Many finishers testify that the challenge is within reach for almost anyone. There are athletes in their eighties who complete Ironman races. In standalone marathons, the Indian centenarian Fauja Singh completed a marathon. Moreover, not all Ironman or marathon finishers have the body composition of Eliud Kipchoge, yet the vast majority still cross the finish line. At the same time, humility is important, as finishing an Ironman is a “small” feat to be savored. Many athletes—even professionals—fail each year, even though it is their profession.
