Quick Answer
Most leg cramps during running are caused by neuromuscular fatigue — your muscles working harder than they are trained for — not simply dehydration. Side stitches come from diaphragm stress, usually triggered by breathing rhythm or food timing. Stomach cramps are a gut response to reduced blood flow and jostling. Each type has a different fix. Treat them accordingly.
The Three Types of Running Cramps
Grouping all running cramps together is the reason most prevention advice falls flat. Leg cramps, side stitches, and stomach cramps have different origins and respond to different strategies. Knowing which one you experience — and when — is the first step.
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| Cramp Type | Where You Feel It | Most Common Trigger | Typical Onset | Primary Fix |
|---|---|---|---|---|
| Leg cramp (EAMC) | Calf, hamstring, quad | Neuromuscular fatigue, going out too fast | Later in run or race | Better training base, pacing |
| Side stitch (ETAP) | Under ribs, usually right side | Shallow breathing, eating too close to run | Early in run, high intensity | Breathing control, food timing |
| Stomach cramp | Lower abdomen, gut | Reduced blood flow to gut, food choices | Any point, especially after fuelling | Nutrition timing, gut training |
What Actually Causes Leg Cramps When Running
Exercise-associated muscle cramps (EAMC) are the sudden, involuntary leg contractions most runners dread. For decades, dehydration and electrolyte loss were considered the main culprit. The research has shifted significantly since then.
Studies using electrical stimulation found that even severe dehydration — up to 5% body weight — did not reliably produce cramps in rested muscle. In contrast, muscle fatigue consistently did. The leading current theory is that EAMC result from altered neuromuscular control: as a muscle fatigues, the inhibitory signals that tell it to relax become less effective, and the excitatory signals that trigger contraction become dominant. The muscle fires without being asked to.
This explains why cramps happen most often in the final stages of a race, in the muscles doing the most work, and almost always in runners who went out faster than their training pace. A 2011 study in the British Journal of Sports Medicine found that increased running speed and pre-race muscle damage were the strongest predictors of cramping in ultra-marathon runners — not hydration status.
Electrolytes still matter, particularly sodium. Replacing sodium (not just water) during long runs in the heat can reduce cramp susceptibility for heavy sweaters. But for most runners in most situations, the primary driver is training load and pacing — not the sports drink.
What Causes Side Stitches When Running
A side stitch — medically called exercise-related transient abdominal pain (ETAP) — is that sharp, stabbing sensation under the ribs, most often on the right side. It affects up to 60% of runners at some point and is more common in newer or less-fit runners.
The most supported cause is diaphragm stress. When breathing becomes shallow or uneven under effort, the diaphragm fatigues and can spasm. The liver sits beneath the right side of the diaphragm, and the ligaments connecting it to the diaphragm can be stressed by the constant downward jolt of running — particularly if you exhale every time your right foot strikes the ground.
Eating or drinking too close to your run is the other major trigger. Fluid and food in the stomach put mechanical pressure on the surrounding tissues, making the diaphragm’s job harder. High-sugar drinks and concentrated sports gels can make this worse by pulling fluid into the gut.
What Causes Stomach Cramps When Running
Stomach cramps during running are a gut response to two things: reduced blood flow to the digestive system and mechanical jostling. When you run, your body diverts blood to working muscles and away from the gut. Digestion slows, and anything sitting in your stomach becomes a problem. For more detail, the stomach cramps when running guide covers the full picture.
How to Prevent Leg Cramps: Training and Pacing Strategies
Because EAMC are primarily driven by fatigue and pacing errors, the prevention strategies are training-based rather than nutrition-based.
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| Strategy | Why It Works | How to Apply It |
|---|---|---|
| Build your training base gradually | Muscles adapt to higher loads over time, reducing fatigue onset | Increase weekly volume by no more than 10% per week |
| Race at your trained pace | Going out faster than training pace dramatically increases EAMC risk | Use the first 40% of a race conservatively — aim for negative splits |
| Taper properly before races | Reduces pre-race muscle damage, one of the top EAMC predictors | Cut volume 20–30% in the final 1–2 weeks before a race |
| Include strength training | Stronger muscles fatigue later and maintain neuromuscular control longer | 2 sessions per week: calf raises, single-leg work, hamstring curls |
| Train in race conditions | Heat and terrain exposure builds adaptation — surprises on race day cause cramping | Do some training runs in similar conditions to your target event |
| Replace sodium on long runs | Especially important for heavy sweaters in the heat — sodium maintains muscle signalling | Consider salt tablets for runs over 90 minutes in hot conditions |
How to Prevent Side Stitches
Side stitch prevention comes down to two things: breathing control and food timing.
Breathing rhythm. A 3:2 breathing pattern (inhale for 3 steps, exhale for 2) helps distribute diaphragm stress more evenly across both sides of your body. The key detail is to make sure you are not always exhaling on the same foot strike — which concentrates impact on one side of the diaphragm. Learning breathing techniques for running can make a significant difference here, particularly for runners who get stitches regularly.
What to do: Practise diaphragmatic breathing during your warm-up. Place a hand on your belly and make sure it rises on the inhale — not your chest. This activates the diaphragm properly before you pick up pace.
Food and fluid timing. Avoid eating a large meal within 2–3 hours of running. Avoid high-sugar drinks or concentrated gels right before starting. If you need to fuel pre-run, a small, low-fibre snack 30–60 minutes out is safer. The how long to wait after eating to run guide has a full breakdown by meal size and run type.
What to do: If a side stitch hits mid-run, slow to a walk, press two fingers firmly below the ribs on the painful side, and breathe with a full, slow exhale. Most stitches resolve within 2–3 minutes.
How to Prevent Stomach Cramps
Gut training is an underused strategy. The gut adapts to running just like muscles do — practising your race-day nutrition plan in training teaches your digestive system to process fuel while under effort. Read more about managing this in the runner’s stomach guide.
The core principles for avoiding stomach cramps:
Allow adequate time between eating and running — typically 2–3 hours after a full meal, 30–60 minutes after a small snack. Avoid high-fat, high-fibre foods in the 2–3 hours before harder efforts. Start with smaller amounts of in-run nutrition and build up your gut’s tolerance. If nausea after running is a recurring issue, check your pre-run food, hydration, and pacing all at once.
Hydration and Electrolytes: What the Evidence Says
Hydration still matters — but in a specific way. The risk is not simply being dehydrated. It is the combination of fluid loss and sodium loss that creates problems on long runs in hot weather. Drinking plain water in large amounts during a long run without replacing sodium can actually dilute blood sodium levels (hyponatraemia) and make cramping and nausea worse.
A practical hydration approach for runs over 60–90 minutes in Australian conditions:
Drink to thirst rather than on a strict schedule. Use an electrolyte drink or tablet rather than plain water when running for over 90 minutes in the heat. For very long efforts, consider sodium-containing options — the salt tablets for runners article covers dosing in detail. In cooler conditions or on shorter runs, plain water is generally sufficient.
Race-Day Cramp Prevention: A Checklist
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| When | Action | Why |
|---|---|---|
| Night before | Eat a carbohydrate-rich dinner 3–4 hours before bed, avoid high fat or fibre | Glycogen stores topped up, gut settled |
| Race morning | Small, familiar snack 2–3 hours before start — nothing new | Avoids stomach surprises, maintains blood sugar |
| Warm-up | 10–15 minutes easy movement, diaphragmatic breathing practice | Prepares neuromuscular system, reduces side stitch risk |
| First km | Start conservatively — aim for 5–10 seconds per km slower than goal pace | Biggest single predictor of cramp is going out too fast |
| During race | Sip electrolyte drink at aid stations for runs over 60 min — avoid gulping | Maintains sodium balance without sloshing |
| If cramping starts | Reduce pace immediately, stretch the affected muscle, resume slowly | Continuing at pace after cramp onset accelerates muscle damage |
How to Stop a Cramp That Has Already Started
The fastest relief for a leg cramp is passive stretching of the affected muscle. Stop running, gently extend and stretch the cramping muscle, and hold for 20–30 seconds. Do not try to push through it — continuing to run with a cramping muscle prolongs recovery and risks a strain.
For a calf cramp: stand with one hand on a wall for balance, place the heel of the affected leg firmly on the ground, and gently flex your toes upward. Hold until the muscle releases.
For a hamstring cramp: sit on the ground with the leg extended straight and reach gently toward your toes until you feel the muscle release.
For a side stitch: slow to a walk, press two fingers into the painful spot, and focus on a full exhale. Avoid shallow, rapid breathing until the stitch passes.
After stretching, walk for 1–2 minutes before returning to running pace. Jumping straight back into effort often brings the cramp back immediately.
When Cramps Are More Than a Training Problem
Most running cramps are benign and preventable. But if you experience cramps that are frequent, severe, or occur outside of running, it is worth checking in with a GP or sports physician. Some medications (statins, diuretics) can increase cramp frequency. Deficiencies in magnesium, potassium, or B vitamins occasionally play a role. Circulatory conditions can restrict blood flow to the legs and cause cramping during exercise. None of these are common causes in otherwise healthy runners, but they are worth ruling out if the training-based fixes do not work over several weeks.
Most running cramps come back to training load and pacing. A coach can look at your sessions, identify where you are pushing beyond your current fitness, and build a plan that keeps you progressing without constantly hitting your limits. If cramps are cutting your runs short, that is a problem worth solving properly.
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FAQ: How to Avoid Cramps While Running
What causes cramps while running?
Running cramps have two main causes depending on type. Leg cramps are most commonly caused by neuromuscular fatigue — your muscles are working harder than they are trained for. Side stitches are caused by diaphragm stress from shallow breathing or eating too close to your run. Both can be worsened by dehydration, but dehydration alone is rarely the root cause.
How do I stop a leg cramp mid-run?
Stop running immediately and stretch the affected muscle. For a calf cramp, stand with your heel on the ground and gently push your toes up. Hold for 20–30 seconds until the muscle releases. Walking slowly for 1–2 minutes before resuming running helps prevent it returning.
How do I get rid of a side stitch while running?
Slow to a walk and focus on deep diaphragmatic breathing — inhale slowly for 3 counts, exhale fully for 3 counts. Press two fingers gently into the painful spot and hold while breathing. Most side stitches clear within 2–3 minutes. Avoid starting your next run with food in your stomach and practise your breathing rhythm from the warm-up.
Do electrolytes prevent running cramps?
Electrolytes help, but they are not the primary fix for most runners. Research shows that exercise-associated muscle cramps are driven mainly by neuromuscular fatigue, not electrolyte deficiency. That said, maintaining sodium and magnesium levels during runs over 90 minutes in the heat can reduce cramp susceptibility, particularly for heavy sweaters.
Why do I only cramp in races, not training?
Race-day cramping is extremely common and almost always caused by going out too fast. Racing at a higher intensity than your training pace puts greater neuromuscular demand on your muscles earlier than they are prepared for. Studies show that runners who start races faster than their trained pace are significantly more likely to cramp in the final stages.
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