What Actually Causes Side Cramps When Running (and How To Stop Them for Good)
Side cramps ruining your run? Learn what causes side stitches, from electrolyte imbalance to dehydration, and what you can do to stop them for good.
You're mid-run, feeling good, maybe even a little proud of yourself, and then it hits. A sharp, stabbing pain in the side of your abdomen that stops you dead in your tracks.
Vibe. Completely. Killed.
That lovely little sensation has a name: a side stitch. These side cramps are your body's way of sending a message, and it usually comes down to three main culprits: dehydration, electrolyte imbalance, and muscle fatigue. When any of these are off, your neuromuscular control (your body's ability to keep everything firing the way it should during aerobic exercise) starts to break down. And side pain is one of the first signs it's struggling.
The good news? This is totally fixable. We're breaking down exactly why side cramps happen and, more importantly, what you can do to stop them from ruining another run.
What Causes Side Cramps
The fancy term for a side stitch is exercise-related transient abdominal pain, or ETAP; a piercing, sharp pain below the rib cage. But why does it happen? Here are a few explanations.
Your Diaphragm Isn't Getting Enough Blood
When you exercise, your body is smart about where it sends blood; it prioritizes the muscles that are working the hardest. The downside? It pulls blood flow away from things it considers "non-essential" in that moment, like your digestive organs. Less blood flow means less oxygen, and when your diaphragm gets shortchanged on both, it can go into a muscle spasm.
Your Abdominal Lining Is Getting Irritated
Inside your abdominal and pelvic walls, there's a lining called the parietal peritoneum. That peritoneal lining has pain receptors (called somatoparietal pain receptors) that are sensitive to stretching and movement.
When your internal organs and abdominal muscles are bouncing around during a run, there's a chance all that movement irritates those receptors and triggers sharp pain in the side of the abdomen. More research still needs to be done on this one, but it's a theory.
The Electrolyte-Cramp Connection
When you're running, your muscles are working overtime. Specifically, electrolytes like sodium, potassium, and magnesium are the crew making every single muscle contraction happen.
Here's how it works at the cellular level, broken down into four simple steps:
- Acetylcholine fires. This neurotransmitter binds to your muscle cells and kicks off the whole process.
- Sodium channels open. This causes ions to flood in, and your muscle contracts.
- Potassium flows out. This signals the cell to start winding down.
- Magnesium steps in. It competes with other ions for binding sites, helping the muscle finally relax.
Every single muscle contraction and relaxation your body does during aerobic exercise depends on that sequence running smoothly.
So what happens when you sweat? You lose electrolytes. And the harder and hotter the conditions, the faster they go. When those levels drop too low during physical activity, your electrolyte levels become unbalanced. Your motor nerves start firing erratically, your muscles may have difficulty relaxing between contractions, and you end up with a muscle cramp or muscle spasm that sidelines your run.
Dehydration Could Be the Culprit
Dehydration is what happens when your body is losing more fluid than it's taking in. It can creep up on you fast from heat, travel, a night out, sweating through a tough workout, or just forgetting to drink enough throughout the day.
When you're low on fluids, your blood volume drops, which means less oxygen actually makes it to your muscles during physical activity.
Your muscles rely on oxygen to produce ATP, which is their fuel source for contraction. Less oxygen in, less ATP out. And when your muscles can't contract and recover properly, you're looking at a muscle cramp.
How To Get Rid of Side Cramps Fast
If you're in the middle of your run, here are two things you can do in the moment to get that sharp pain under control.
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Practice deep breathing
We're talking belly breathing, otherwise known as diaphragmatic breathing. This is where you breathe deep into your belly instead of your chest, which can help support mobility and better muscle fiber recruitment.
It may not make the side pain vanish instantly, but it supports your posture and overall endurance, which means less opportunity for that stitch in the side to show up in the first place. Try inhaling slowly through your nose, letting your belly expand, then exhaling through pursed lips. Do that a few times and see how your body responds. -
Dial back the intensity
Nobody wants to hear this one, but it works. When you're pushing hard, your muscles are under more stress, burning through oxygen faster and losing electrolytes and fluids at a higher rate. That's a recipe for a muscle that can't keep up.
Dropping your pace (even just for a few minutes) gives your body a chance to catch up, restore some balance, and get back to functioning the way it should. Think of it less as giving up and more as a strategic reset. Once the side of your abdomen stops screaming at you, you can pick it back up.
Does Salt Help With Cramps?
Sodium plays a pretty important role in how your body supports fluid balance and nerve signaling. When you sweat, sodium is one of the first things to go, and losing too much of it during aerobic exercise or endurance activity can throw off the fluid balance your muscles need to function properly.
So in situations where you're sweating heavily or putting in a long run, getting some sodium back in does matter.
That said, salt alone isn't a magic fix. Side cramps and muscle soreness during physical activity are rarely just a sodium problem; they're usually a full electrolyte problem. Potassium and magnesium are all part of that same muscle contraction process we talked about earlier. Your best bet is balanced electrolyte intake rather than focusing on salt alone.
Cramp Prevention Protocol
The best fix for side cramps isn't what you do mid-run; it's what you do leading up to it. And a big part of that is making sure your electrolyte intake is actually where it needs to be before you lace up.
Maintaining proper electrolyte balance during exercise supports muscle function, nerve signaling, and hydration, which are all the things that keep cramps from crashing your run. So what does that actually look like in practice? It starts with knowing your daily targets based on how active you are:
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Sodium
Aim for up to 2,000 mg/day, or between 300 and 600 mg per hour of prolonged exercise.
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Potassium Target
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Magnesium
Most adults need 300–400 mg/day, with athletes trending toward the higher end.
These ranges aren't one-size-fits-all. How much you sweat, the climate you're training in, and how hard you're pushing all affect how fast you burn through electrolytes. Running in July humidity hits differently than a winter treadmill session, and your intake should reflect that.
An electrolyte packet is a great way to get your electrolytes in. Instead of cobbling together a handful of supplements and hoping for the best, Waterboy's Workout Hydration formula gives you a balanced electrolyte blend built to support your muscles before, during, and after your run.
It's got 3x the electrolytes of the leading competitor, zero sugar, and a formula designed to support recovery. Is it a miracle? No. But if your side cramps are coming from dehydration and electrolyte imbalance (which, as we just covered, they probably are), it's a pretty solid place to start.
Additional Prevention Strategies
Here are a few more habits worth building into your routine:
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Warm up properly before physical activity
Jumping straight into a hard run is a great way to invite a side cramp. Dynamic warmups (where you're actively moving through a range of motion rather than holding a single stretch) help prepare your muscles for the demands ahead and support better posture and musculoskeletal function.
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Build your core strength
Your core muscles do a lot more than look good. A strong core improves your stability while running, which means your body works more efficiently, fatigues less quickly, and puts less stress on your muscles.
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Stay consistently hydrated
Water is essential, but it doesn't replace the sodium and electrolytes lost through sweat. If you're only drinking plain water before and during a run, you're only solving part of the problem. Consistent hydration means keeping your electrolyte levels balanced throughout the day, not just chugging water right before you head out the door.
When Side Pain Might Be Something More Serious
Most of the time, a side stitch goes away once you slow down, breathe, and stay hydrated. But there are some symptoms worth paying attention to that could signal something more serious.
If the stabbing pain sticks around for an extended period even after you've rested, that's your cue to contact a healthcare provider. And if it's showing up alongside nausea, vomiting, or abdominal distension (aka your stomach looking swollen), don't brush it off. Those are signs that your body may be trying to tell you something, and medical advice is the right call.
The Bottom Line on Side Cramps
Side cramps are one of the most common complaints in running and also one of the most preventable. At the root of almost every side stitch is the same handful of culprits: dehydration, electrolyte imbalance, and muscle fatigue.
Small adjustments add up fast; smarter hydration, a proper warmup, building your core strength, and keeping your electrolytes balanced all help. Check out Waterboy's full lineup and find the formula that fits your run.