Cramping: What you need to know

Last month I had a few athletes competing in the Jonkershoek Mountain Challenge. Most finished without any major issues, but one athlete finished with a near collapse at the finish line from what appeared to be dehydration. No other issues other than dizziness and a general feeling of being unwell. We called the medics who fed her water with a well known hydration powder filled with electrolytes. It seemed like dehydration was a common theme on the day as temperatures were well above the norm for early winter in Cape Town. Almost every runner who I spoke with complained of either feeling dehydrated or of cramping. This made me wonder: why do some of us cramp while so many others never do? I have a long history of cramping, which made my mind wonder.

I remember my first 50 km mountain ultra; it was a cold, winter morning, with a light drizzle falling on my waterproof jacket and hood at 05:30 in the middle of the Franschoek mountains. I remember looking around at the other runners, amazed at how seemingly nonchalant they appeared by the cold and wet conditions, knowing that in a few minutes the starting gun would go off and we would all head out into the vast mountains for over 6 hours. I remember the feeling of adrenaline as the gun went off, as well as the feeling of reluctance as it began to wear off. I remember feeling great until 20 km in when the clouds opened up and the temperature dropped to near freezing, and having to summit a mountain while not having much feeling in my fingers and toes. I remember the first cramp during that climb, that first feeling of intense pain and discomfort in my groin as I took every excruciating step toward the summit. I had experienced cramping before during my rugby playing days, but nothing like this. The elevation increased and the cramps got worse, but it was only on my way down when the cramping began to spread. First to my quadriceps, then my hamstrings, and then my calves until it felt like a game of muscular musical cramps. I finished the race, barely, but that day will forever be ingrained in my psyche as the day I properly met my nemesis: cramps.

Fast forward two years and three Ultra marathons later, and I am sad to say that I am still yet to figure out why I cramp. It has improved, and I can run for far longer distances before the first signs of cramping set in, but they are still there waiting for their opportunity to cast their debilitating spell on my skeletal muscle, rendering me helpless to the grip of their paralyzing spell. I have tried drinking more water, adding electrolytes, adding glucose drinks, eating more solids, to even taking a longer taper with more rest days, with some success. So what causes cramping? For that, we take a look at the research.

What is cramping?

Cramping, or more specifically exercise-associated muscle cramping (EAMC) can be defined as a syndrome of painful skeletal muscle spasms that occur during or immediately after physical activity, with the most common sites being n the calf, hamstring or quadriceps muscles. [1] There are a number of theories as to what causes cramping, with the most common being that heat, dehydration, and electrolyte depletion are the main causes of EAMC [1]. Let’s take a look at there one by one:

Electrolyte depletion

More than 100 years ago the theory was first reported that athletes who experienced cramps had low levels of blood chloride, magnesium, calcium and high levels of potassium. However, there have been a few scientific studies that show no relationship between blood electrolyte balance and EAMC [2] In one study, the researches looked at the sweat sodium concentrations in athletes who cramped and those that didn’t cramp under various testing conditions. What was found is that the sodium sweat conditions of normal ‘non-cramping’ athletes was in fact higher than the athletes with a history of cramping, debunking the theiry that a high sodium loss is one of the causes of EAMC. [2]


This hypothesis also has its roots more than 100 years ago, when cases linked mine workers to high sweatng and cramping from presumably dehydration, [2] and is still a very common cause cited by athletes and researchers. However, a look into the literature didn’t identify a single published study which linked dehydration to acute EAMC, and that dehydration is, in fact, not associated with EAMC. [2] In a study of 72 runners competing in an ultra-endurance road race, there was no significant difference between pre-race and post-race body weight, per cent change in body weight, blood volume, plasma volume, or red cell volume between runners who cramped and those who didn’t cramp, debunking the theory that hydration may contribute to cramping. [3]

The altered neuromuscular control hypothesis

Muscle fatigue, which results in altered neuromuscular control, was first proposed as a cause of EAMC in March 1996 when a study of 1383 marathon runners showed that 60% of runners self reported that muscular fatigue caused their EAMC. [2] Over the past 10 years, more studies have been done exploring this, all basically pointing to the fact that cramping only occurs when the muscles are very fatigued either from high intensity, long exercise duration, decreased muscle energy, hot/humid conditions or poor conditioning [2]. Also, many studies show that EAMC happens far more in hot conditions, and the term ‘heat cramps’ was coined in the late 1930’s. Scientists have studied cramping in hot conditions for years, and the electrolyte / dehydration hypothesis have been disproved, and therefore there has to be some mechanism that high heat fatigues the muscle and disturbs the neuromuscular firing another way.

In summary, the literature supporting the electrolyte and hydration hypothesis to cramping is sparse, with only 18 studies done before 2009 making anecdotal connections to these factors. The basis for the ‘altered neuromuscular control’ theory is, comparatively, based on laboratory models of cramping, animal testing, as well as field studies, and therefore a far more likely culprit.

Looking at the above and my training history, I tend to agree with the neuromuscular fatigue theory. My cramping has not improved drastically regarding the severity, but what has changed is the amount of time and the intensity of exercise; I can train longer for harder before cramping than I did 2 years ago. What this tells me is that my muscles are becoming conditioned to this extremely great demand, and therefore are creating adaptive methods to delay this muscular fatigue.

Or maybe, just maybe, I should accept my fate and learn to deal with the cramps. With that said, if you ever see me lying on the side of a trail not being able to move from cramps, please at least drag me into the shade :)

And with that, I say farewell.

Happy Running

Coach Robert


[1] Schwellnus MP, Drew N, Collins M (2010). Increased running speed and previous cramps rather than dehydration or serum sodium changes predict exercise-associated muscle cramping: A prospective sohort stury in 210 ironman athletes.

[2] Schwellnus MP (2009) Cause of exercise associated muscle cramps (EAMC) - altered neuromuscular control, dehydration or electrolyte depletion?. Mr J Sports Med 43: 401-408

[3] Schwellnus MP, et al (2003) Serum electrolyte concentrations and hydration status are not associated with exercise associated muscle cramping (EAMC) in distance runners. Br J Sports Med, 38:488-492