Running Cramps: Myths and Realities

Ah, cramps. That moment when your calf muscle decides to turn into a brick in the middle of a half marathon. Every runner dreads them, yet they're one of the most misunderstood phenomena in sports physiology. Most explanations that have been repeated for decades are now being challenged by research. I've delved into what the studies truly say.

⚕️ Disclaimer: I am not a doctor. What I'm sharing here comes from my scientific readings and my experience as a runner.

"You didn't drink enough" — Really? A Persistent Myth

The most common explanation: dehydration and electrolyte imbalances. This theory dates back to the 1920s (observed in salt mine workers). The idea: sweating causes a loss of sodium and potassium, which would disrupt muscle function.

However, recent data significantly weaken this explanation. A study on participants in the South African Ironman (Schwellnus et al., 2011) found no significant difference in sodium levels between those who cramped and those who didn't. And if dehydration were the cause, we'd experience generalized cramps everywhere — yet they almost always affect the most heavily utilized muscles.

That doesn't mean proper hydration is useless. Severe dehydration degrades performance and worsens fatigue. But simply drinking more, by itself, doesn't protect against cramps.

The Real Lead: Neuromuscular Fatigue at the Heart of the Problem

The theory with the most credibility today is that of neuromuscular fatigue (Professor Martin Schwellnus). Essentially, when a muscle becomes overly fatigued, the nervous system loses its ability to properly regulate contraction. The muscle then contracts involuntarily on its own.

This theory effectively explains what we observe in the field:

• Cramps affect specifically recruited muscles.
• They primarily occur late in a run or when hitting the marathon wall.
• Runners who start too fast are more vulnerable.
• Passive stretching provides immediate relief (it stimulates an inhibitory reflex).

Magnesium: Little Evidence, Lots of Marketing

Magnesium is often seen as the miracle cure on running forums. Everyone recommends it. However, systematic reviews (Garrison et al., 2012, Cochrane database) conclude that the evidence is insufficient to recommend it against exercise-induced cramps.

A nuance, however: a true magnesium deficiency (biologically diagnosed) can indeed cause cramps. But this is a different clinical situation. And the placebo effect is powerful: if you are convinced that magnesium helps you, the perceived benefit can be real without being pharmacological.

A varied diet (green vegetables, nuts and seeds, whole grains) generally covers needs without supplementation.

Prevention: What (Probably) Works to Avoid Cramps

Since neuromuscular fatigue appears to be the key factor, prevention primarily involves preparation and effort management.

Train Specifically

A well-trained muscle resists fatigue better. If you're preparing for a marathon, long runs and sessions at a specific pace condition your muscles. The number one risk factor remains running above your current fitness level.

Warm Up Properly

A progressive warm-up prepares the neuromuscular system. It doesn't directly prevent cramps, but it delays the onset of fatigue.

Start at the Right Pace

Starting too fast is the best way to cramp up at the end. A pace based on your estimated finish time reduces the risk. An appropriate fueling strategy also helps delay overall fatigue.

Strength Training

Strengthening calves, quadriceps, and hamstrings increases their fatigue resistance. Eccentric exercises (step-downs, single-leg squats) seem particularly relevant.

What To Do When It Still Happens

• Slow down immediately: reduce intensity to relieve the muscle
• Gently stretch: hold for 15-30 seconds, it activates the inhibitory reflex
• Briefly massage: mechanical pressure can help
• Resume gradually: accepting that you might need to adjust your time goals downwards

Interesting fact: recent studies are exploring the effect of pungent substances (vinegar, pickle juice) which might stimulate an inhibitory reflex via the mouth. Preliminary results are interesting but not yet solid enough.

What We Don't Know Yet

Why do some runners never cramp, while others do so systematically? Genetic factors likely play a role. The interaction between central (brain) and peripheral (muscle) fatigue is still poorly understood.

In summary, cramps are likely multifactorial: neuromuscular fatigue plays the primary role, potentially aggravated by dehydration and individual factors. The best strategy remains adapted training and careful effort management during a run.