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Stomach Problems – Why Better Running Form Can Also Improve Your Fueling

Published on by Ingo Kruck
Running Form and Stomach Problems - Guest Post - Lechrunning
11
June

My name is Ingo Kruck, founder of Lechrunning.de and a passionate ultratrail runner, running technique coach, and trainer, and I’m writing this guest post for Squeezy. In my daily work with athletes, everything often revolves around two main topics: How do I get the most out of my body, and how do I optimally fuel it for distances ranging from half marathons and marathons all the way up to 100 miles?

Let’s be honest: When we’re getting ready for a big event, we suddenly turn into little nutritionists. We test which gel tastes best (and stays down), whether we prefer to chew energy fruit gummies or bars, and debate among ourselves whether water, an isotonic drink, or a carbohydrate drink is the holy grail at the aid station. But who among us seriously thinks about things like osmolality beforehand? Yet that’s exactly what—the concentration of dissolved particles in the drink—acts as the gatekeeper to your stomach and is often the main cause of serious stomach problems.

And what about running form? For most people, it goes completely unnoticed. We usually don’t start thinking about stride rate, foot strike, and—above all—our own posture until our knees start acting up, our shins are inflamed, or our pace simply plateaus despite hard training.

What very few people know: These two systems—your stomach and your legs—are connected by the exact same pathway in your body. No one adjusts their energy intake based on their running style, obviously. But improved running form is like a free software update for your digestive system. It takes the mechanical stress out of the system and makes it much easier for your body to actually utilize those hard-earned carbohydrates.

Here’s a deep dive into the science of sports to explain why your energy metabolism and biomechanics are inextricably linked—and how you can finally put an end to stomach problems while running.

 

1. Biomechanics of Foot Strike: How “Cube Running” Can Cause Stomach Problems

Running technique guru Wolfgang Schweim (Runningwolf) once came up with a brilliant analogy when asked what sets four-time triathlon world champion Patrick Lange apart from the competition in biomechanical terms: “Patrick rolls across the asphalt like a ball; the others are more like dice!”

During physical exertion, our body switches to pure survival mode: blood flow to the gastrointestinal tract is reduced by up to 80% (a condition known as ischemia) in order to direct oxygen to the working muscles. In this sensitive state, the digestive system becomes extremely sensitive to purely mechanical stimuli.

The problem: overstriding and vertical oscillation. Anyone who hits the ground with an inefficient, choppy running style—that is, “cubing” their heel well ahead of their center of gravity (overstriding)—sends a shockwave through their torso with every step that’s 3 to 5 times their body weight. You don’t need a calculator to imagine what that does to your muscles and joints. On asphalt, this also amounts to monotonous microtrauma for your stomach. On the trail, with its roots, jumps, and uphill and downhill sections, your abdomen turns into a shaker. The fluid is constantly being shaken, which massively slows down gastric emptying and absorption in the intestines and often triggers acute stomach problems.

The benefit of your running technique: A smooth, flat “roll” through the midfoot and a slightly quicker cadence (step frequency) reduce the up-and-down bouncing. The softer the landing, the calmer your stomach will be. Your fueling suddenly goes much more smoothly because easily digestible carbohydrates can pass through the stomach without this constant mechanical disruption.

By the way, this is exactly where your footwear comes into play: Highly cushioned Max-Cushion shoes aren’t just a sofa for your feet—they also act as a giant mechanical filter for your abdominal cavity. Their thick midsole absorbs the initial impact before the shockwave can travel through your skeleton and jolt your internal organs. Especially when your legs get heavy during long ultraruns and your natural muscle cushioning starts to fail, this passive shock absorber saves your digestive system from a total knockout—but be careful: even the softest heel in the world won’t save your fueling if you still stomp into the ground ahead of your center of gravity. In the end, proper running form always beats the gear.

 

2. Posture: The physical stranglehold and the direct path to stomach problems

In order for the gastrointestinal tract to break down energy and release it into the bloodstream, it needs two things above all else: physical space and oxygen. A collapsed running style literally takes the wind out of the system’s sails.

The problem: The “fatigue slump” The longer the race, the heavier your head feels. We stare at the asphalt or, on the trail, focus only on the half-meter in front of our feet (sometimes that’s a good thing to avoid a crash, but not always). The upper body slumps at the hips. On steep uphills, we then add the popular habit of resting our hands on our thighs. The sports-biological consequence: This hunched posture compresses the abdominal cavity. Intra-abdominal pressure rises, the entrance to the stomach gets squeezed (hello, acid reflux!), and the diaphragm gets blocked. Breathing becomes shallow, oxygen deprivation in the intestines increases, and stomach problems make their presence known politely but firmly. Especially in ultra-distance races, the moment quickly arrives when the only thing that matters is not seeing your food again.

The Benefit of Your Running Form A proud, upright posture with a slight forward lean from the ankles keeps your chest open like a barn door. You breathe deeply into your abdomen, supplying oxygen to your intestines and giving your organs exactly the space they need to digest your gels without any trouble.

 

3. Arm Movement: Why Rotating Shoulders Can Trigger Stomach Problems

We run with our legs, but our arms set the pace. They control the rotation of the upper body and stabilize the pelvis. What almost no one knows: they have a direct connection to your internal mucous membranes.

The problem: Crossing your arms in front of your chest. Tense arms that frantically cross in front of your chest (a classic occurrence during the final kilometers of a marathon or when running off-road without poles) create a constant, unnatural twist (torsion) in the torso. These rotational forces pull directly on the ligaments that support the intestines. Under full load, this leads to mechanical irritation, side stitches, or those painful gastrointestinal issues (like the proverbial foam party in the colon) that unexpectedly force you into the bushes.

Your Running Technique Tip: Shoulders down, relax! Let your arms swing smoothly in a straight line at a 90-degree angle in the direction of travel. This stabilizes your core, reduces shear forces on your abdomen, and allows your natural bowel movements (peristalsis) to do their job undisturbed.

 

4. Tactical Timing: How to Use the Terrain to Avoid Stomach Problems

In trail running, in particular, the physical demands and terrain are constantly changing. Runners who stubbornly stick to a set schedule for fueling often make tactical mistakes that come back to haunt them an hour later. When your stomach starts acting up, it’s often not the food’s fault—the timing was just off.

  • Uphill – Time for a snack: With power hiking, there’s no flight phase. Zero vertical braking forces, zero jolts. Mechanically speaking, your stomach gets a break. This is the perfect time for a quick energy boost or a snack like Squeezy Energy Bars. (Exception: When the terrain gets so technical that you need your hands for climbing.)

  • On the flat – The fluid rhythm: A fast, steady pace, predictable jostling. This is where the classic Squeezy Energy Gels really shine. Thanks to their optimized, low osmolality, they pass through the stomach particularly quickly and won’t weigh you down even at a fast pace.

  • Downhill – Keep your hands off the buffet! Eccentric muscle contractions and steep drops send shockwaves through your skeleton. Your internal organs are subjected to extreme compression. Anyone who pops a gel during a technical downhill run risks it getting stuck in their stomach along with a lot of swallowed air and immediately causing acid reflux. The rule here is: Full focus on the ride! Save the snacks for before or after the downhill.

 

Side Note: The Overfueling Trap – Why the 100g Myth Often Leads to Stomach Problems

While we're on the subject: Even the smoothest, gazelle-like running style won't save you if you ignore a fundamental biological limitation. I'm talking about overfueling.

Somehow, a dangerous myth has taken hold in the running community lately: “If 60 grams of carbs per hour is good, then 100 grams or more must literally make me fly!” Um, no. Just because the world’s elite consume 120 grams (or more) per hour doesn’t mean that eating the same amount will automatically turn you into Kilian Jornet or Tigist Assefa.

Does everyone really need 100 grams of carbohydrates? Absolutely not! Your body has only a limited number of transporters (think of them as little “taxis”) that can carry carbohydrates from the intestines into the bloodstream. For a relaxed, scenic ultra at a comfortable pace or a solid 4-hour marathon, 60 to 90 grams per hour is often plenty. For trail ultras in the 100-kilometer and 100-mile range, 90 grams is now recommended. 

The magic threshold of 100 grams or more only gives you a real performance advantage if you’re running at your absolute limit. We’re talking about massive, sustained intensity close to the threshold, or when you’re running a fast ultra and have to do everything in your power to keep your glycogen stores from running dry so you can maintain a fast pace. If you consume these amounts without the corresponding muscular exertion, your gut transport system gets backed up. The sweet mass piles up, starts to ferment due to bacteria, and draws water into the intestines. You can guess that this doesn’t have positive consequences either, because once again we’re left out in the sticks with massive stomach problems.

The secret is called “Train the Gut.” If you really need those massive amounts of carbohydrates for your race, you have to prepare your stomach for it just like you would a muscle. That’s the famous “Train the Gut” principle. You can’t spend weeks during training drinking only tap water and then suddenly open the floodgates for 100 grams or more of carbohydrates on race day. Your gut has to be well-trained!

I do this very deliberately in my own training: In early summer, I incorporate fast, intense hill workouts and fartleks on undulating terrain, during which I deliberately train my stomach to handle over 100 grams of carbohydrates per hour under heavy strain. This works perfectly fine—provided you don’t pour chemical junk into your system. That’s exactly why, during exertion, I exclusively use Squeezy products like Refiller gels or the new Energy Drink Basic Formula , which contain no unnecessary additives and are absorbed very quickly. For most athletes, however, this process isn’t something you can master with just a few runs. Increasing your intake to >100 g of carbs per hour can take months or even years, and what you don’t keep training will be lost again.

Bottom line: Figure out exactly how much food your specific race pace requires, train your eating habits just as hard as your legs—and then roll across the finish line smoothly and with a happy stomach!

 

Bottom line: Your running form is the best way to prevent stomach problems

Ultimately, it's simple math: the less efficient (and less smooth) your running style is, the more energy you burn per kilometer.

Proper running form significantly reduces your body’s glycogen consumption. Conversely, this means that during long-distance runs, you simply need to consume fewer grams of carbohydrates per hour to maintain the same level of energy. And the less you have to strain your digestive system under full load, the lower the risk of dreaded stomach problems or a drop in performance.

So a smooth running style not only protects your joints, but is also the best way to maximize your energy intake!

Training tip: Learn how to lay the biomechanical foundation for an efficient, stomach-friendly running style in the hands-on Art of Running seminars at Lechrunning (exclusively in Southern Bavaria; additional dates throughout Germany available at Runningwolf). This neurologically highly effective system automates your individually perfect movement pattern far more effectively and sustainably than dull running drills or haphazard self-experimentation with YouTube tutorials ever could.

 

Happy Running

Ingo from Lechrunning.de

 

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