At the 2025 Western States, Kilian Jornet perfectly demonstrated how to test different methods in training. “When I first went to Western States, before, I didn't really do any preparation. It was just like, okay, it's another race — I’ll just go and figure it all out in the run. Now, we tried to understand the demands of the race when it comes to everything — metabolically, neuromuscularly, and on the temperature — and then try to do the training and strategy for the race depending on those specific demands.”

Fueling over a long distance means understanding what works for you. For 100 miles there is no formula. Practice, experiment, and adapt to establish a strategy that’s comfortable and effective. It  takes time to get it right. A fueling strategy should not be left to the last moments of training. If the body can take it in training, it can take it in the race. But you won’t know until you try different strategies on your longer training runs, enabling the body to get used to fueling while running. Fueling while trail running can take even more practice. The undulating terrain and constantly changing effort can put additional strain on the stomach.

By his own admission, Kilian is not suited to the Western States course. “It’s probably one of the last trail races I would choose only for its course and conditions. Probably that is why I wanted to do it, because it doesn’t fit me and that’s why it is exciting to train for.”

Over 100 miles, comfort is everything. Not just for the physical kit — clothing and shoes — but more importantly in your gut. Science has shown that training our guts with certain amounts of sports nutrition decreases the likelihood of gastrointestinal distress on race day. GI discomfort is a significant inhibitor to performance. By fueling training with the right amount of carbohydrates per hour, our bodies can adapt and get used to it. In this aspect of training, Kilian is meticulous. “You have to do a lot of practice with your fueling to make sure it's okay in your stomach. Like everything, especially in nutrition, you need to do the practice and to see that it works well — to understand that everyone's physiology is absolutely different.” And it means that not everything he does — that works for him — would necessarily be right for another athlete. Mastering the art of fueling is about getting to know your own body. It’s something that Kilian has a lot of experience with.

Nobody has access to the same training facility, terrain, or environment. For Kilian, training in Norway to prepare for a race in the heat of California presented a unique challenge. “In the past year I started doing some heat training and saw great improvements, so I was somehow confident that it would be possible to prepare for the race doing heat training while living in Norway.” Consistency was key because adaptation takes time. “During the race I never felt hot, and I felt in control — that I could push. Which means that the strategy was good and in the days after, I feel well recovered. It makes me think maybe I could have started pushing a bit earlier."

Specificity is also important. Kilian trained and prepared a fueling strategy that wasn’t just about the specific demands of Western States — it was about enabling his unique physiology to perform in that environment. “I wanted to gain a bit of weight before the race, to have some additional storage, because I don’t have much fat reserve. We were thinking that if I use around 8,000 calories in the race and I might be able to consume five or six thousand calories over that time, that it could be helpful to have two or three thousand more calories in fat available on my body. I was trying to get a bit more fat in before the race and found that an easy way to consume fats, even while running, was through olive oil or coconut fats. But you absolutely have to do a lot of practice with that to make sure it's okay in your stomach.” 

In the race Kilian’s strategy was heavily refined to suit him. Kilian explained that, although it’s known for being a hot race, it starts at altitude where it can be very cold, so the course requires a special approach. “I didn't want to be overcharging my stomach and my intestines from the beginning. So I tried to be the most fat-efficient for the first five hours (mixing avocado, coconut oil, nuts, dates, banana, overnight oats, cacao, and beetroot) and then being able to move to mostly carbohydrates towards the end. Fluid intake was around 0.5 liters per hour.”

As the temperature increased and Kilian moved into the notoriously hot canyons, he shifted his fueling. Fluid increased to 1 liter per hour, with some sodium, with soft bars in the downhills (when it was slightly easier to chew) and Maurten Gel 160 in the uphills.

From Foresthill to the finish, Kilian moved to a purely carbohydrate strategy, with Maurten Gel 160 in a Gelflask, consuming every 30 minutes at a rate of 110g per hour. He maintained fluid intake of 1 liter per hour with 1.5gr of sodium.

Third place and the fifth fastest time in history — nearly 80 minutes faster than his previous finish was an exciting result. It left Kilian feeling motivated by the progress he was able to produce. “Even if we are aging, we can still improve with more understanding of our body, our capacities, and just to have a better plan on how we need to train and how we need to prepare for the race day. At the finish I felt strong and that was a nice feeling — it motivates me more."

All imagery and quotes provided by Maurten.