When the body refuses to race
Some time between 2023 and 2024, I started having relentless GI distress in ultras, and often in training as well. I’ll spare you the details (maybe another time in another format). It was unpredictable and brutal. The sudden kind of gut chaos that makes performing at a high level impossible. It felt like wading through cement. I hired the best sports dietician (and would work with him again any day). We dialed in my fueling. I tracked macros, hydration, sodium, etc. I went through all the basic tests. Everything came back fine. If nothing was wrong, why did it keep happening?

That’s when I started reading about nervous system regulation and discussing this with my coach. The mechanisms: the vagus nerve, gut-brain signaling, parasympathetic downshifting, the way chronic stress and endurance strain can layer on top of past trauma, creating a body that feels unsafe in safe conditions. The more I learned, the more it made sense. My gut wasn’t failing, it was my response, to accumulated stress, and a nervous system that, while outwardly functional, was locked in high alert every time I ran. I didn’t need a different diet or gel. I realized that already.

A dysregulated nervous system doesn’t always feel like a panicking gut. At times, it feels like tunnel vision, or nausea that won’t quit, or a spike in heart rate on an easy climb, a sudden collapse in mood that makes a runnable section feel unbearable. Or tears for no clear reason at 3 AM, headlamp bouncing, brain fried. For me, dysregulation shows up subtly at first: stomach growling, my brain at high alert, scanning for potential bushes, cramping, loss of concentration and flow. The storm comes from inside.

Polyvagal theory, introduced by Dr. Stephen Porges, adds an important layer to the idea of “rest and digest.” It shows that the parasympathetic system has two branches. One, the ventral vagal pathway, supports social connection, calm presence, digestion, and adaptability. The other, the dorsal vagal branch, is linked to freeze, shutdown, and collapse. It’s still parasympathetic, but it’s not restorative. That matters for athletes because what might feel like emotional numbness, detachment, or sudden energy collapse mid-race might not be bonking, or even sympathetic overdrive. It might be a dorsal vagal response: your body’s way of saying, if I can’t fight or flee, I’ll disappear. You’re still moving, but the lights are half-off inside. Knowing the difference between these states can help you respond more wisely, not by pushing through, but by finding the gentlest way back.

My nervous system stuck in the red, overactivated, spun out, unable to recover, to climb down the ladder to the green zone. The sympathetic fight-flight loop doing its job a little too well. It wasn’t a mental weakness, or a fueling error. It was biology in overdrive. Nervous system regulation, I’ve learned, is the art of returning: to breath and grounding, to sensation, and presence. It’s the act of purposeful downshifting. Of recognizing when your body is screaming “danger” even when everything seems normal and according to plan.

It’s not always the workouts that break you. It can be the accumulation and the layers. Sleep debt with a tempo on top. A hard conversation from the day before. The subtle whiplash of switching from email to forest, back to email again. Our nervous systems generally don’t separate any of this. It doesn’t care that the intervals were in Zone 3. If I arrive to the trail already activated and bracing, it doesn’t matter how carefully the plan was written, the body interprets load differently and in total.

What nervous system regulation taught me is that I needed to stop training through disconnection. The closer I stayed to myself, my breath, pace, sleep, body, the more resilient I became, and less likely to crack from things some call “just stress.” Now I call it what it is: a message. One I try to answer, before the body breaks.

A lot changed when I began to treat regulation not as something that just happens, but as a living skill, one I could carry in my pocket like a soft stone, something to turn over in my hand when the wind picked up, or my stomach flipped, or my mind wanted to disappear. The more I practiced, the more I saw: regulation is endurance. During races, the lonely ones, or the ones where everything goes sideways, it’s the difference between spiraling and finding back your rhythm. I am happy to share some of my experiences and practices with you here.

Steady in the storm
It was during SwissPeaks 360 (now 380) in 2023, about 60 kilometers in, when the first spiral began. I had come into the race in probably the best shape of my life. Just a few weeks earlier, I’d won a local ultra, small, but meaningful, and I felt ready and confident. While I’m no stranger to travel or to racing solo abroad (that was my usual practice), the days leading up to the start were more taxing than I’d admitted to myself. I’d been in Switzerland and Chamonix, acclimatizing, cheering friends at UTMB, navigating new environments, last-minute logistics, accommodation changes, all on my own. I told myself it was fine. But my body had already started tallying the stress. Likely before I stepped on the plane.

The race itself began smoothly enough. I held back deliberately, sitting around tenth place as planned. With no crew, I was juggling a massive drop bag, quite necessary for a 360 km point-to-point, and that, more than anything, probably started to wear on me. I felt steady, but a bit wound up. Still, without pressing, I began to move through the field, swapping spots with the frontrunners. Two wrong turns came while I was in first place (easy to make, with sparse flagging). A growing unease I couldn’t quite shake. I was running not with confidence but with static in my head.

Things unraveled quickly. I slipped into the red, my stomach stopped processing, and my vision began to tunnel very quickly, until only about 20% remained. I could still see enough to continue, but the world had shrunk. Every part of me was stretched thin. My nervous system had tipped into full alert: shallow breath, racing thoughts, a low-level panic humming beneath the skin. One moment I was climbing strong, the next I could hardly walk the flats. By the time I reached the next aid station (after still another 1,300 meters of vert) no amount of calories could bring me back. I had mentally checked out anyways.

A mere three days later, I lined up for another race, hoping to salvage the fitness I still carried. No sleep, and hardly any rest, but with zero expectations, I figured maybe things would be different. Yet, almost on cue, 60K in, everything spiraled again. Same gut shutdown and no clear trigger, just a body that had stopped listening, or maybe one that had never been heard in the first place. I continued to finish the race (for another 100 km, maybe the hardest thing I have every done) and all the signs became visible. It was not hard to miss, to be honest.

“Nervous System Says No”
What happened at SwissPeaks wasn’t a mystery of willpower or fitness. It was physiology. When your nervous system tips into sustained sympathetic overdrive, fight, flight, or freeze, systems shut down in predictable, protective ways. Blood gets redirected away from the gut, vision narrows, digestion slows to a halt, muscles tighten, breathing becomes shallow, thoughts start looping, and decisions that felt easy before now feel impossible. This isn’t mental weakness. It’s a coordinated survival mechanism; one that doesn’t mesh well with ultra running.

The vagus nerve plays a central role here. It’s the longest cranial nerve in the body, running from brainstem to gut, and it’s responsible for modulating the parasympathetic nervous system. Your “rest and digest” branch. When vagal tone is high, you’re more adaptable: your heart rate slows quickly after stress, digestion hums along, and you can return to equilibrium faster. When vagal tone is low, or when chronic stress pushes you into sympathetic dominance, the system gets stuck. You may look composed, but internally you’re in a holding pattern, always bracing and rarely recovering.

When I first began digging into the research (from the likes of Dr. Linnea), I found myself circling one core idea: the body can’t distinguish between psychological stress and physiological overload. It treats a missed aid station, an argument with your partner, or a night of fragmented sleep, and a 3,000-meter climb, with the same neurochemical alarm bells. Cortisol rises, blood glucose spikes, digestive function slows, the immune system becomes temporarily suppressed. These are adaptive in short bursts. Over long races or long seasons, they begin to wear grooves into your internal wiring. That’s where the idea of “nervous system dysregulation” really lands: it’s not just stress, it’s getting stuck in stress.

When you encounter stress it activates the Hypothalamic-Pituitary-Adrenal (HPA) axis, a hormonal system that governs the release of cortisol and other stress hormones. That’s useful in short bursts, but when this axis is chronically overactivated, it starts to fray the body’s internal balance: appetite, mood, energy, sleep, and digestion all take a hit. Long ultras layered on modern life can stretch the HPA axis into constant vigilance, where recovery never quite catches up.

In endurance athletes, this chronic dysregulation often shows up as a collapse in heart rate variability (HRV), a sign that the parasympathetic system isn’t doing its job. HRV measures the subtle beat-to-beat variation in your heart rate, and higher variability indicates a more responsive and resilient nervous system. Lower HRV, especially when paired with poor sleep or persistent fatigue, means your system is leaning too far into sympathetic drive, running hot, even at rest. In some studies, lower HRV has been linked not only to overtraining but to higher injury rates, poor decision-making, and GI distress during exercise (note: HRV isn’t a perfect oracle, and I recommend to look for patterns, not panic-worthy dips, use it as a conversation with your system, not a verdict).

That’s where nervous system regulation comes in. It’s not about avoiding stress, it’s about giving the body tools to return to safety. Over time, I began layering in practices that improved vagal tone and widened my stress window. For example (and I will go into more in a different essay):
– Breathwork, like slow exhales or 4-7-8 breathing or 1:2 ratio of inhale to exhale can shift your body into parasympathetic mode within minutes, activating the vagus nerve directly. 
– Humming, chanting, singing, or even softly talking to yourself when alone on trail all stimulate the vocal cords and signal calm through vagal pathways. 
– Barefoot running or walks after hard efforts, can ground you, literally, through proprioceptive feedback. Applying deep pressure to hands or thighs is another way.
– Cold exposure, for me the most successful practice, builds what’s called “vagal flexibility:” your body’s ability to come back from activation quickly and cleanly.
– Co-regulation, sharing space with someone calm, like a partner, pacer, even a kind volunteer, can regulate your system by proximity. Human bodies are relational. We feel each other’s state before we hear words.

Most of all, I started tracking my mood, irritability, gut function, decision fatigue. You don’t have to use every tool. You don’t have to be perfect. What I’ve learned, what my nervous system taught me the hard way, is that regulation isn’t a side dish, it’s the plate everything else is served on. Without it, everything else slides off, eventually. These are physiological access points. They make fitness useable, especially when things get hard. And of course in ultras, things always get hard

Training the System Beneath the System
Before you train your aerobic system or musculoskeletal system, you train your nervous system. Whether you realize it or not. Your nervous system is the gatekeeper and first responder. The filter that determines how your body interprets and processes stress. We like to think of training stress as mechanical: volume, calories burned, etc. From a biological standpoint, all of that is meaningless unless your nervous system can tolerate it as safe. That’s the threshold many of us overlook: the perceived safety. When your nervous system perceives threat it shifts into a defensive mode: muscles tighten, breathing constricts, blood moves away from the gut, your body prioritizes survival.

Your nervous system is always scanning for cues of safety or danger, long before your conscious brain catches on. This process is called neuroception, and it’s based on pattern recognition in your environment and within your body. A certain kind of noise, a tightening in your jaw, a sudden crowd at an aid station, all of these can register as “threat” even if they aren’t. When neuroception misfires or is hyper-sensitive, you may find yourself panicking or shutting down in moments that don’t seem stressful on paper. That’s why regulating state is so essential. Because performance depends not only on what’s happening, but on what your system believes is happening. Belief, here, isn’t a thought. It’s a felt signal from the body.

This is what Dr. Linnea calls “the hidden cost of dysregulation”: the body may still complete the workout, but it might not interpret it as productive stimulus. Instead of a training effect, you get a stress effect. Cortisol spikes, HRV drops, recovery becomes incomplete, and the next session feels sluggish, not because you’re unfit, but because your system never got the memo that it was safe to rebuild. This is where it gets tricky: dysregulation doesn’t always feel dramatic. It can show up as vague underperformance, flat legs, training plateau, trouble sleeping, you might tell yourself you’re not motivated enough. Or it might not show any clear signal.

That’s why and how I’ve come to see daily regulation as one of the most foundational form of training. Here’s a peak at what a nervous-system-informed training week might look like in practice:
– Morning light within 30 min. of waking, try to get outside, even for a short walk, to catch direct sunlight that anchors your circadian rhythm and dampens cortisol spikes later in the day
– Breathwork daily, 3–5 min (or longer): use 4-7-8 breathing or simple 1:2 inhale-to-exhale ratios, especially pre-run or before bed. The long exhale stimulates vagal tone and helps downshift from “go-mode” into “recovery-mode.” When I have my routine together, I do it in the morning.
– Post-run reset, because the end of a run ≠ end of the stressor: after harder sessions, take 5 min. to lift your legs up, close eyes, one hand on chest and belly, to signal to your system, “we’re done now.”
– Tech curfews: at least one hour before bed, shut down screens, sometimes imperfectly, but enough to notice the difference in heart rate and sleep quality. Less blue light, less stimulation, more deep sleep. This is a hard one for me.
– Nourishment on time: not just what you eat, but when. Skipping or delaying meals is a fast track to sympathetic overload. Eating at consistent intervals, even small snacks, reminds the body that resources are abundant.

These aren’t “hacks” or performance add-ons. They’re what allow performance to land. Like trying to build a house on shifting ground, training without a regulated foundation might hold up for a season, but eventually, it buckles. When the nervous system is calm, the body becomes adaptable. Not just in training, but in life. You can run harder without breaking. You can rest more deeply without guilt. You can feel fatigue without fearing it means something’s wrong. It changes how you respond to effort, and how you recover from it. It builds a baseline of fitness and trust. That, more than any workout, is what keeps you in this for the long run.

The Gut-Brain-Run Axis
Before wrapping up this first essay on nervous systems, let’s turn back to what got me here in the first place. At the center of this story is the enteric nervous system, sometimes called the “second brain.” It’s a dense network of over 100 million neurons embedded in the walls of your gut, capable of operating semi-independently from the brain. It controls digestion, nutrient absorption, the mechanical movement of food through the intestines (a.k.a. motility). Crucially, it’s also deeply connected to your autonomic nervous system, which governs whether your body is in fight/flight mode (sympathetic), or rest/digest mode (parasympathetic).

This toggle, between sympathetic and parasympathetic states, is mediated in large part by the vagus nerve, a bi-directional superhighway that links brain and gut. When vagal tone is high, digestion continues, blood flow stays steady, and nutrient absorption stays functional. When your vagus nerve is underactive, or your sympathetic system is dominant for too long, the GI system goes offline: motility slow, gut lining becomes more permeable, nausea and cramping become more likely, and the body simply deprioritizes digestion, because it thinks you’re under threat. This isn’t mere theory or your stomach being stubborn, it’s biology.

We focus on what to eat. Maybe the better question sometimes is: what state are you in when you try to eat it? Especially in ultras, the gut doesn’t operate in a vacuum. It reacts and is part of large system, right there with your lungs, legs, brain and heart. When the nervous system is steady, the gut doesn’t just survive the race, it becomes part of your strength.

Here are some ways you can support gut regulation during a race:
– Pre-fuel breath reset. Before you eat/slurp a gel, especially during a high-effort part, pause. Try 3 slow, nasal breaths: inhale for 4, exhale for 6–8. You’re signaling safety. You’re bringing blood flow back to your stomach. It only takes 20 seconds, but it can make a gel more digestible.
– Walk while fueling, not after. Digestion happens best under light movement, not at a dead stop or under max exertion. Walk with purpose, but keep your breath relaxed. Use this rhythm to help food move down.
– Train gut function AND gut state. During long runs, don’t just test products. Practice how you eat: slow down, breathe, chew, mimic the race environment and add in regulation tools (see next post), walk while fueling, stand still to eat early in the day. Teach your gut that fuel = safety.
– Reduce incoming sensory load. Your nervous system has a bandwidth limit. In overstimulating moments (crowded aid stations, spectators, loud music, blinking headlamps), minimize non-essentials, close your eyes, create a pocket of calm before trying to eat.
– Ground before you sit: This might sound weird, but when stopping at an aid station, touch a rock, tree, or the ground for a second. Give your body sensory feedback. Grounding through touch or pressure gives your proprioceptive system a signal of safety. It helps downshift sympathetic tone.
– Orient to safety (visually or audibly). Vagal tone improves when your body believes it’s safe. Look up, scan the horizon, lock eyes with a volunteer, and say something kind aloud to yourself. These tiny moments reduce perceived threat and help digestion stay online under effort.
– Don’t override early signals: respond. If you feel the first hint of nausea, dry mouth, food aversion, etc.: pause. Don’t stuff more in or suppress it with something else. Ask: What’s going on in my system? Then take one regulatory action. Gut problems escalate when ignored.

This was the essay I needed years ago. Maybe you do too, not because GI distress or spiraling thought loops are universal, but because nervous system overload is. Modern life doesn’t tend to taper for your race. In ultras, the system that’s underneath the system, that tells your gut it’s okay to digest and your brain it’s okay to feel, that’s really worth training.

Many athletes carry old stress in their bodies, (like overt trauma, chronic adversity) and that history doesn’t disappear when you toe the line. Trauma doesn’t always look dramatic; it can show up as a nervous system that’s slightly hypervigilant, a gut that shuts down under effort, or a mind that catastrophizes mid-race. For some, ultras become a mirror and amplifier: revealing the ways we’ve learned to override ourselves, to disconnect in order to endure. While running can be therapeutic, it’s not therapy, and without tools to recognize when past stress is hijacking the present, we risk mistaking dysregulation for failure, when it might just be our body asking, again, to be heard.

If you’ve made it this far: thank you. I’ll be following up with a second piece soon, focused on the practices that support this work; how to activate your parasympathetic nervous system during racing and reset your stress response in motion. Maybe I will also write about navigating the mental landmines of catastrophizing and intrusive thoughts when they inevitably arise. Let’s be honest: regulation is not only physical. Sometimes the hardest thing to digest is a thought.

Until then, I’d love to hear from you: Have you experienced a spiral like this? Do you any of this in your training? What regulation tools have helped you most? Drop me a message, share this with someone whose gut has been through it lately, or leave a comment.