Training for the Uphill Athlete, the training bible by Kilian Jornet and Steve House, Extracts

In Training for the Uphill Athlete, Steve House, Scott Johnston and Kilian Jornet have joined forces to share their decades of combined training experience. Whether trail running in the mountains or ski mountaineering, this training manual, edited by the Alpine Mag team for publishers Guérin-Paulsen, offers the results of the work of these exceptional athletes and trainers, as Kilian Jornet confided himself. Extracts.

Up ! Guérin-Paulsen, 375p., 2020. Extrait du chapitre 2 – La physiologie des sports d’endurance.

Don’t skip over these important pages too quickly, in your eagerness to read on about how to train in order to beat Kilian in his next race. You won’t find it. As we regularly reiterate in this book: there is no single recipe to maximise your physical fitness. You are the only one who can optimise your perfect programme. These opening chapters have been written precisely because of the individual nature of training. We know you need this information in order to make the right decisions about your training.

 In this chapter, we look at the type of physiology which enables you to produce the energy required for endurance sports. A basic understanding of how this physiology works will give you the intellectual framework to be able to make decisions during your training and implement your own training plan or someone else’s. Following any old programme blindly without understanding the underlying principles will hinder, or even undermine your performance. The following considerations deal with the physiology of sport.

Developments in endurance

Over thousands of years, several different Homo species evolved alongside one another, co-existing with and rivalling Homo sapiens as hunter-gatherers. The fact that we won the evolutionary race is due in part to our species’ endurance capacity. Rarity used to be the normal state of things and competition for calories meant consuming lots of time and energy; therefore prehistoric man’s metabolism evolved to give those who used the precious calories most efficiently the best chance of passing on their genes to the next generation.

Average days comprised long hours searching for food while expending the least energy, interspersed with short bouts of intense effort during the critical point of hunting, when it was necessary to control a targeted prey or outperform another predator or scavenger. The food intake of the first hominids was rich in animal protein and fat, with a small amount of plant-based complex carbohydrates. Prehistoric man’s physiology developed a calorie fuel tank in the form of fat reserves (both intramuscular and beneath the skin, lipids) to store excess calories consumed during periods of abundance. Fat would feed our ancestors during these long days hunting and gathering and gave them a better chance of survival during food shortages. We evolved to be able to store large quantities of fat in order to survive several days of famine before our body suffers any permanent damage. Well-accustomed hunter-gatherers could hold out longer between meals and intensify their activity thanks to lipids, thereby saving the rare and precious reserves of glycogen from carbohydrates. Our ability to replenish muscle glycogen reserves quickly during rest periods (in just a few hours) presents another interesting aspect. This is not the case for most other animal species; that is how we would wear out our prey as we would only need short periods of rest.


Lipids are complex molecules with an array of chemical links, and each link contains energy which can be used. Even a slender, well-trained endurance athlete can store up to 100,000 calories in the form of easily accessible lipids. Carbohydrates, which are simpler molecules with fewer chemical links, produce around half as many calories per gram as lipids. Our capacity to store carbohydrates is much lower, no more than 2,000 calories even for well-trained athletes. During periods of excess, our body’s strategy is to store all the calories we consume, regardless of where they come from, in the form of lipids. From a purely physiological point of view, this explains the modern-day rise in obesity; a lot of people consume an abundance of high calorie food yet are rarely exposed to food shortages.

According to a popular theory in evolutionary biology, the first hominids used their endurance and hairlessness (which enabled them to avoid suffering from overheating unlike their prey) to their advantage in order to hunt down their next meal to exhaustion. This helped them to rise to the top of the food chain despite their relative physical weakness. Endurance is what enabled our ancestors to approach and kill much more powerful animals, which were simply too exhausted to fight back. The theory also argues that the protein-rich diet, made possible through hunting, increased the capacity and complexity of their brains. This led to a cognitive revolution, which itself generated cultural progress and the development of characteristics which were subsequently passed down to us. Hence it follows that you are able to read the words on this page precisely because our species survived by using its inherent capacity to cope with long periods of low to medium intensity effort. We are the result of an evolutionary process which predisposes us to endurance.

Kilian Jornet training in Romsdal, in Norway, two weeks before leaving for Everest in March 2017. ©Jordi Saragossa

Endurance and fatigue

Endurance training aims to improve our capacity to run, climb or ski over a prolonged period. Ultimately, endurance is limited by our body’s predictable reaction to fatigue due to these activities. It is fatigue which restricts endurance. That is why it is essential to offer a brief description of this state. In athletics, endurance is the maximum sustainable pace (whether speed or strength for example) that an athlete can maintain throughout the duration of an event before fatigue forces them to lower the pace.  Fatigue in our sports can be seen through shorter, slower-paced strides. Several interconnected physiological systems come together to influence endurance performance during events of different durations and intensities. For example, the intensity involved in running half a mile vertically is very different from running a 30-mile race. Yet both events will test a runner’s specific endurance / fatigue limit. The type of endurance required and the kind of fatigue felt vary depending on the event.

We don’t need an expert in sport physiology to tell us that fatigue slows us down. The right training makes us more resilient to fatigue and thereby prevents us from slowing down. We are highly complex organisms and a whole host of adjustments to several bodily systems is required in order to improve our resilience to fatigue. To keep it simple: this dreaded slowing down which we all loathe is primarily caused by our body’s inability to meet the energy requirements related to exercise. This limitation can be caused by a drop in or accumulation of certain metabolites, as well as a weaker motor nervous system signal.

Essentially, we can divide these different physiological systems into groups, as below. We create a model, an artificial limit and segregate these systems which are in fact intimately interconnected and interdependent. This simplified model is commonly used scientifically to break down complex ideas and systems into their component parts, which can then be better understood. The art of training draws in part on understanding the interconnection and interdependency of these systems.

The oxygen supply system

The heart, lungs and blood vessels comprise the oxygenation system responsible for providing oxygen (O2) to all the body’s cells, including those in the skeletal muscles during exercise.

Lungs. While we may feel ‘out of breath’ during intense workouts, healthy lungs are in fact oversized in relation to our requirements and have a gas exchange capacity which is more than enough. The surface area of human lungs equates to half a tennis court.

Heart. A great many scientific studies have shown that it is the heart’s capacity to pump which is the main obstacle to O2 intake in healthy individuals. Yet, while the lungs stop developing after puberty, the heart can be trained to increase its flow per minute, which allows more O2 to reach the muscles. This adaptability may be limited by our genetic predisposition and any endurance training history. The heart reaches full maturity during teenage years, developing most quickly and most actively during this period. Young people, just like older individuals starting from scratch, may notice quick, significant changes in their heartbeat because the heart muscle is very easy to train, subject to any predetermined genetic issues. The limitation in stroke volume sets the absolute upper limit of O2 intake and therefore acts as a limit to aerobic endurance. For mature athletes (who have a long history in endurance practice), training may offer no or little change in their stroke volume. (…)


How I began as an athlete / by Kilian Jornet

Kilian Jornet and his sister take a break in the Pyrenees. ©Kilian Jornet Collection

The house where I grew up was surrounded by mountains and forests. The first time I saw a TV I was five years old. When my little sister and I weren’t in school, we would play outside all the time, climbing trees and jumping off rocks. For children, spending time outside is a unique experience: being in the outdoors, in forests and snow, getting used to this kind of mountainous terrain.

My Mum and Dad were both mountain enthusiasts. My father was a mountain guide and had quite a traditional view of mountaineering; he taught me the techniques, the safety precautions, and to respect this environment. My mother was a climber and a long-standing runner, who while a little less organised, was very experienced. She took to the mountains much more freely. She liked to move as quickly and lightly as possible.

When I was three, we started climbing peaks as a family. We would go cross-country skiing and my parents would carry our downhill skis for the way back. That was my introduction to skimo. When I turned five, we would climb up to 3,000 m (9,842 ft) and practise on glaciers while roped together, with crampons and ice axes. This was also the time I completed my first straightforward corridors. Looking at the photos from that time, the helmet on my head is so big I look like a mushroom.

At ten years old we backpacked across the Pyrenees, a 40-day trek. Every year we would do something like that. That is how I learned about endurance and what it takes to do a multi-day hike. When I was 13, my Mum started taking me on longer outings in the mountains, and sometimes I didn’t take enough to eat or drink. I remember spending nearly 16 hours without food or water and having to lick water off the rocks.

It was at that time that I started skimo training. I had already done long cycling races and 80-kilometre (50-mile) courses from one mountain hut to another, without following any kind of particular training plan. I joined the Catalan sports training centre, and my trainer would send me a monthly programme explaining what I needed to do every day. There were two trainers, and maybe ten athletes per trainer.  From the age of 13 to 17, I learned about the notions of muscle volume, interval training, strength training, recovery as well as mountain conditions and techniques.

During this time I also went to school, so I would train early in the morning or at the end of the day, and at lunchtime I would go to the gym or run. I used weekends to do longer runs. Sometimes I would go to school by bike, with my skis in my backpack, and after school I would cycle 60 kilometres (37 miles) to the snow front, I would ski for a couple of hours and then cycle back home again. Other times, I would run the 25 kilometres (15 miles) to and from school. My trainer would often reproach me for doing too much, despite the fact that I would tell him that cycling was just my means of transport. I was so focused on training, obsessed even. (…)

Read our interview with Kilian Jornet about the publication of Training for the Uphill Athlete