The body can do it. The stomach cannot.
A quick note upfront: This post is a deeply personal, data-driven analysis of why my stomach regularly shuts down during solo ultra-races, even when my fitness and motivation are spot on. I am sharing my concrete body and performance metrics here, alongside the physiological connections between the nervous system, stress, and digestion. Ever struggled with stomach issues on long distances? Then this post is for you.
A Search for Clues: From the First Finish to the Stomach Shutdown
I still remember exactly how excited I was when I registered for the first Atlas Mountain Race in 2020 together with Tobias. I had no clue about structured training, sleep deprivation, endless days in the saddle under heavy strain, pace control, nutrition strategies, race tactics, or bicycle and gear optimization. It was all the more astonishing for me when we made it to the finish line and successfully completed it. On my own, I would never have dared to do it.
And in that enthusiasm, we immediately signed up for the next adventure: the Silk Road Mountain Race the following year. This time, however, we dealt more thoroughly with all the topics surrounding such events. And physically, we were also significantly fitter. That—together with a good strategy—successfully brought us to the finish line at Lake Issyk-Kul in 2021 as well.
I enjoyed this focus on ultra-bikepacking. But there was a problem that accompanied me through all these years and that I have only really understood now.
After the two races with Tobias, I wanted to try it solo for once and started at the Bohemian Border Bash Race in 2023. Physically, I was very well prepared and highly motivated. But after 1,000 km, I unfortunately had to give up because I developed saddle sores and simply could not keep riding. At the same time, however, I also noticed that I needed to work on my pacing and required a different strategy than just going full attack. So I had to learn to understand my body a bit better. And my mindset at the time was absolute focus on success in these races. That was very important to me, because I also wanted to prove to myself that I could do it alone.
A while ago, I published a post about DNFs here, in which I also emphasized that one must thoroughly examine the reasons and also factor in that such races might simply not be for everyone.
And so I also analyzed the DNF at the BBBR 2023 and tried to learn from it. My focus back then, however, was heavily geared toward strategies to prevent saddle sores. I neglected other factors in the process.
Then came the Trans Balkan Race and another DNF. I had simply misjudged the race, was neither mentally nor physically ready, and had additionally injured the ulnar nerve in my hand.
My analysis back then focused more on the lack of performance capacity, a potentially wrong choice of bike, and improper mental preparation.
So I worked even harder on myself, cranked up the training intensities, and became more capable. But I wanted to test this without race pressure first and started at the Grenzsteintrophy on my 50th birthday in 2025.
Actually a perfect tour, because you determine the pace and time for the route yourself. And yet I put too much pressure on myself, approached the pacing incorrectly, made mistakes with nutrition, and ran completely out of steam after 800 km. I simply couldn’t eat enough, and that pulled the plug on me. A real beginner’s mistake—one might think. But more on that later.
My learning from it: physically I was absolutely capable again, mentally prepared as well, but I had to learn to eat under heavy load. So I began training that specifically, added the nutrition component to my training, and tried various options: liquid carbs, gels, bars—between 80 and 100g of carbohydrate intake per hour. You have to get your gut used to that.
In the autumn of the same year, I spontaneously rode in the North2Peak and wanted to see if I had learned my lesson. And yes, it went fantastically – but also because I didn’t ride alone, but always in company, ultimately as a duo with Sandro. And so I was able to finish successfully and had zero performance or nutrition issues.
That was a real breakthrough for me, because I thought I had finally found the holy grail of my performance capacity. And of course, I wanted to show that not just to myself, but also to you. As self-confident as I am – being able to prove it is nice every now and then.
So this year I registered for the Italy Divide, which started in Pompeii at the beginning of May and led 1,400 km up to Lake Garda. For this, I had adjusted my training once again, wanting to get even fitter and especially stronger in the mountains. That paid off, and I made it very smoothly over Vesuvius and the Abruzzo mountains, through Rome, and into Tuscany. Unfortunately, I had to drop out there due to family reasons. But I was fit and would have made it to the finish line by May 9th. On the route, I eventually bumped into Christopher, and we rode together and enjoyed Italy. So again a pair setup where things worked well.
However, I wanted to do something else this year, as I had trained a lot and felt fit. But above all, I was investigating a suspicion as to what could be the reason for my DNFs over the last few years. And I wanted to test that, so I spontaneously registered for the Bohemian Border Bash Race again. The starting location is easy for me to reach, and I simply fancied the beautiful landscapes. This was to be my testing ground: physically more than sufficiently prepared, mentally too—let’s see how far I get and whether I can transfer the good feeling from Italy Divide to this. The question was simple: Can my body do this – solo, under race pressure, over several days, with sufficient food?
I can ride hard and long, and I had previously prepared with a training block in the Bavarian Forest (BBBR terrain) featuring 7,750 meters of elevation gain and a long-distance ride to Leipzig (round trip) totaling 900 km. My Coros said “Optimized,” and I had a good feeling.
What happened then
Day 1 was really good: 220 km, 4,623 meters of elevation gain, average heart rate 129 bpm, and 16.1 km/h. I rode in a controlled manner and didn’t want to overdo it, which is why I ended the day according to plan after just 220 km. During the day, I was able to fuel well with liquid carbs, gels, a few bars, cocoa, and Cola. But in the evening at the restaurant, I couldn’t get a single bite down. Just a little dumpling with sauce. Nothing more was possible.
Day 2 was still solid: 202 km, 3,736 meters of elevation gain. I tried to eat more, noticing that it wasn’t enough: bananas, a filled baguette, Snickers, gels, liquid carbs, Cola. But my stomach remained shut; several bars and gummy bears didn’t get far and came right back out. I tried to reduce the pace to calm my stomach, but that didn’t really work. Then came the confirmation: the average heart rate was down to 111 bpm, which was too low and indicated a lack of energy supply. In the evening, I forced myself to eat a few potatoes and chicken meat. But more simply wasn’t possible.
Day 3 was survival: 168 km, 4,155 meters of elevation gain. The pace collapsed, from 16.1 to 12.9 km/h. Not because my legs went on strike, but because no more fuel was arriving. I literally crawled up some of the climbs, feeling completely limp. At lunchtime, I tried to eat some tomato soup and gnocchi. But even here, only to a limited extent. In the evening, another attempt, but I only managed half of the schnitzel, nothing else. The body rejects solid food; what I try to eat anyway either doesn’t really go in—or comes right back out.
In my desperation, I tried taking in carb powder from the bottle and decided to take a longer break. Timewise, that was still acceptable, and if I succeeded in calming my gastrointestinal tract so that it allowed food again, I might be able to continue riding.
Day 4 was the scratch: 78 km one way to Český Krumlov to Checkpoint 4, and after that, it was over.
The numbers behind it
I calculated my calorie intake for those days retrospectively. And if you look at the numbers, you can see exactly what happened:
A 16,731 kcal deficit in four days: that is not just eating a little bit too little, but a structural deficit. However, that is also typical for ultras.
Bengt Stiller once said that right from the start of such exertions, you are always consuming yourself.
You cannot compensate for the daily calorie deficits at all, also because the body cannot absorb that much. And what works well in an ideal training environment or on shorter rides simply doesn’t work under conditions like the Bohemian Border Bash: 13–16 hours in the saddle, always under time pressure to cover the distance, constantly under strain. Liquid carb intake alone isn’t enough there – you simply need solid food too.
And now we need to talk about concrete body metrics so that you can understand this in my case as well.
Physically, at 51 years old, I am fitter than ever:
- I have +8,000 km and over 50,000 meters of elevation gain on the clock this year
- my measured metabolic age is 32
- my FTP is 290W
- my muscle mass percentage is 83%
- my body fat percentage is 13.4% with 2.8 visceral fat.
And the scales confirmed after those days in Bohemia: I lost two kilograms of fat in four days. One kilogram of fat corresponds to roughly 7,700 kcal. And honestly, that is too much for such a short period.
What actually happened there?
The reason lies in the nervous system, which has two modes:
- The sympathetic nervous system: fight or flight.
- The parasympathetic nervous system: rest and digest.
When you sit on the bike for 13–16 hours a day under race pressure, your body keeps the sympathetic nervous system continuously activated. It interprets this as an ongoing state of emergency. And in a state of emergency, the body doesn’t need digestion, it needs muscles. Therefore, blood is diverted away from the digestive organs and pumped into the legs. The stomach receives less blood flow and then shuts down its operation.
In sports medicine, this is called Exercise-Induced Gastrointestinal Syndrome, or Ex-GIS for short. In the context of ultra-bikepacking, however, this has not been researched very extensively, and my symptoms of food refusal should therefore be viewed as purely anecdotal.
However, people don’t like to talk about it much because it is considered a personal failure or interpreted as a weakness. Yet it is simply a predisposition and varies individually.
My body reacts to these strains with a shut stomach. Others, for example, can no longer sleep properly because the sympathetic system fires constantly. I was able to observe that at this year’s BBBR as well.
And both foster side effects like saddle sores, since at some point the strength needed for body stabilization is lacking, and one tends to make compensatory movements that can lead to such seating problems. Or to cramps and knee issues. For example, I ride quite differently in the saddle uphill when I am fit and powerful. My riding position is completely different than when I am just trying to hold on to the bike because my strength is running out.
However, given that I couldn’t eat properly, covering over 600 km and around 13,500 meters of elevation gain isn’t bad at all.
What occupies my mind the most: the legs could still have kept going. The head too. But without energy from food, it eventually comes to an end. That was no longer a question of willpower.
From nutritional consulting, one often hears tips in this context regarding the optimal glucose-fructose ratio or the osmolality of sports drinks.
In structured training or short events, that can certainly be tested and controlled perfectly. But the reality of an ultra-race looks different: you eat whatever is available. When the body has to process Snickers, Cola, cold pizza, or gas station baguettes after ten hours on the bike, that puts extreme strain on the stomach anyway.
Add the race-induced sympathetic stress to that, and the system breaks down completely for me—even with liquid carbohydrates that still worked flawlessly in training. I can’t stand the sight of them anymore, and I get nauseous.
Yet I tried everything: nutrition training, small bites every 30 minutes, carb powder, gels, liquid calories. In training or short tours, that worked fine. But in the race, after two or three days on the bike, none of it helped anymore.
And in retrospect, this running on empty due to insufficient food intake was always a component in all my DNFs. Often masked by other reasons, such as a sore butt, a damaged hand nerve, or physical exhaustion.
In my analysis, there was an interesting observation for me that I had been making for a while, but which now consolidated: when I don’t ride alone, but together with someone else (who matches roughly my performance level), I manage fine and finish.
With a partner, I had a corrective element that decelerated me at times, made sure that I took breaks and ate something.
Neurobiologically, this is called Social Buffering: the presence and co-regulation of a partner measurably dampens the stress axis in the brain. This lowers the release of stress hormones like cortisol and calms the sympathetic nervous system. Above all, it keeps the vagus nerve active—the very system that maintains gastrointestinal blood flow and digestion. In solo mode, on the other hand, your own brain carries 100% of the cognitive load and control responsibility, which switches the body into continuous flight mode much faster.
For me, someone who actually prefers to be alone, an even tougher realization.
Why “just ride slower” doesn’t help
Now one could say: then just ride as if a partner were there. Yes, gladly. I know this reaction, of course, but it misses the point.
First, the time limit in such ultras often doesn’t allow you to ride slower at all. At the BBBR, you have to ride at least 187 km per day to stay within the limit. Actually more than 220 km on the first days to have enough buffer for the tough stages at the end. That means whoever rides significantly slower risks missing the cutoff.
Second, slower does not mean less stress. That is a crucial point, because it means more hours under the exact same stress. If I ride only 12 km/h instead of 15 km/h, I need more time for the same distance, which equals more hours of continuous sympathetic stress. The stomach doesn’t recover then; it suffers longer.
Third, slower is sometimes even more exhausting. A lower pace can be less efficient than a higher one. The body sometimes works harder at 14 km/h than at 16 km/h. I often notice this when I try to ride with slower riders. That strains me more than riding my own pace.
One could object that at a lower intensity or different wattage output, digestion ought to work after all. But in practice, that falls short: the problem in a solo race is not primarily an excessively high physical watt intensity, but the continuously high mental stress level. Via the brain-gut axis, the permanent psychological tension hits the stomach directly. The sympathetic system stays on continuous fire, completely regardless of how fast I ride.
The problem is therefore not the intensity, but also the duration. And that cannot be reduced far enough in a solo ultra-race with a strict time limit to give my GI system enough room to recover.
The body can do it. The stomach cannot.
That is the sentence that occupies my mind the most. And it is now a clear realization.
My body is ready and can deliver all of it. Only my GI system is the problem, albeit under one very specific condition: solo, multiple days, maximum race pressure, not a moment of genuine relaxation.
At the Atlas and Silk Road Mountain Race with Tobias, at the North2Peak with Sandro, at the Italy Divide with Christopher, everything worked—with a more relaxed pace, culinary breaks, without great race pressure. The difference wasn’t fitness, but the stress level. And with it, the mode of my nervous system.
What I make of this
Of course, I am not stopping riding. That’s nonsense. But I am adjusting now: (long) solo ultra-races with strict time limits are not my format. Not because of the legs or the head, but because of my digestive system, which after several attempts has clearly told me: Not like this.
Fortunately, however, the whole topic of bikepacking consists of such ultra-races and challenges to only a very small degree. We shouldn’t be fooled by the omnipresence of it all on social media.
I am therefore returning to my roots now and doing bikepacking tours again that challenge, that have mountains and technical terrain, but without the race pressure that keeps my sympathetic system continuously on high alert. Those will again be tours right on my doorstep, cycle tours around the world, but also bikepacking events with more time—and then gladly with a partner as well.
Who relates to this?
I know this topic is rarely discussed. A DNF often quietly disappears into one’s own race history. Sometimes people say afterward “I grew from it,” and sometimes people don’t talk about it at all.
If you have experienced something similar, I look forward to your comment. And also any kind of tips and tricks on how to deal with it.
And to anyone who can contribute medically to this: you are very welcome!
