Running Cramps Part II: What Causes Cramping?

Written by Curb IvanicUncategorized


Running cramps are all too common and runners are bombarded with different theories as to what causes cramping and what to do about it.

If you’re a “screw the science” type person and don’t care what causes running cramps, go directly to Part III of this series and learn how to avoid them.

But if you’re a bit like me and want to know how stuff works then read on.

Different Types of Cramps

As outlined in the chapter on muscle cramps in a medical textbook, different factors and mechanisms may be at play with different types of cramps.

So I want to be perfectly clear that I’m talking specifically about exercise associated muscle cramps (EAMC) in healthy runners who aren’t taking prescription meds or have specific medical conditions.

It’s still common to hear dehydration or electrolyte deficiency as the culprit for cramping. As I’ve described in Part I and previously there are some pretty big holes in these mechanisms causing running cramps.

The major problem with these theories is that empirical data shows there isn’t any significant difference in hydration or electrolyte status between runners and triathletes who cramped versus those who didn’t cramp.

So if it’s not your lack of hydration or electrolytes that causes cramping what does?

Science Says…

Fatigue and neuromuscular dysfunction seem to be the primary mechanisms behind EAMC.

One clinical paper stated that cramps are associated with “muscular fatigue and shortened muscle contraction.” An earlier paper cited “disturbances at various levels of the central and peripheral nervous system” as a possible mechanism for cramping.

An interesting case study described how strengthening one triathlete’s glutes cleared up a history of hamstring cramps. The hamstrings were overworking which lead to premature fatigue and cramping. By making the glutes stronger, they took on their fair share of the work during running so the hamstrings didn’t have to work as hard and the cramps didn’t reappear.

Another experiment looked at how the signals from certain receptors in muscle tendons affected incidence of cramping. When these signals are weak or absent, cramps occur more often. If the signal to relax a muscle increases then cramping stops or doesn’t occur.

It’s important to note that when muscles are in a shortened state, these contraction-inhibiting signals are silent or at a very low level. And when do most cramps occur? In muscles that are in a contracted (shortened) position.

Further evidence for fatigue causing cramps is described in a medical paper from Argentina. The authors recommend “preventing premature fatigue by means of appropriate nutrition and adequate training.”

Running faster was also associated with a greater risk of cramping as seen in a study of Ironman triathletes and another study involving ultramarathon runners. The triathlete study also showed that a previous history of EAMC predisposed athletes to cramping while the ultramarathon study showed muscle damage as being a risk factor as well.

Taking these factors together – running faster; muscle damage and a history of EAMC leads to premature muscle fatigue and as we’ve seen from previous research this increases the chance for cramping.

What to Do?

Now that we know what causes running cramps the next question is how do you prevent muscle cramps from occurring and what can you do to stop a cramp if it occurs.

For the answers, see Part III of this series.


I'm Curb

Curb is a performance running coach with 20+ years experience working with athletes of all levels.

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