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Tuesday, November 20, 2007

Muscle Cramps: Part I

Theories and Fallacies of muscle cramps

As promised in yesterday's post, today we kick off our latest series - Muscle Cramps. We hope that none of you did cramp in the middle of the night, as we mentioned yesterday! Though if you did, we're sure you stretched your calf and avoided the temptation to point your toe!

This is a follow-on from our series on Fluid Intake and Dehydration, and as we were preparing to write this series, we realised that there may actually be even more nonsense and blatant lies in the media than there were for dehydration!

Conflicts of interest revisited

In the dehydration series, we dealt with the very obvious conflict of interests that arise when a company which manufactures and sells sports drinks become the company who are funding and then performing much of the research on fluid and exercise. This is what happened when Gatorade created the Gatorade Sports Science Institute, and began funding research studies all over the USA, that rather unsurprisingly told the world that thirst was not enough, and you just had to drink as much as you could.

Can you imagine Gatorade issuing the results from those first studies saying to people "Folks, we've tested the sports drinks, and we don't have much evidence that you really NEED them. You'd most likely be fine without them, but hand over your money and buy your Gatorade at the counter anyway". An unlikely scenario. Of course, it was never as simple as that, and as we tried to explain previously, some of the early lab-based science was actually sound, but its application became the problem. More than this, the manner in which the research was compromised, becoming a form of shameless endorsement for the sake of sales in subsequent years was the ultimate problem. But that was all covered in our previous series, for those who are interested...

Muscle cramps - even more pervasive mis-marketing, but a complex issue

The same marketing vs scientific integrity debate exists for muscle cramps. The industry that has sprung up around the muscle cramp issue has spread far and wide. It includes Gatorade, who advocate the use of their drinks to replace the loss of salt which is, according to their research, responsible for the cramp in the first place! But more than this, there are dozens of products that claim to prevent cramp - next time you are in a pharmacy, take a look at the range - everything from gels, to creams, to pills, to effervescent tablets.

The two broad theories for muscle cramps

All these products work off the same premise - the put back the electrolytes that exercise will take out. And it's the loss of those serum electrolytes, the theory goes, that are responsible for the cramps during exercise. This theory, over 100 years old, is one broad category of theories for muscle cramps.

The second theory is that muscle cramps are caused by a 'malfunction' in the control of the muscle by the nerves - an abnormality of neuromuscular control which is caused by fatigue.

Our objective in this series is to look at these two theories, beginning with a bit of groundwork and history...

Defining cramp

Perhaps one of the first things to do is provide a definition for cramp, as well the usual disclaimer that we cannot possibly cover all the possibilities and scenarios in this series. Firstly, cramp has been defined as a "spasmodic, painful, involuntary contraction of the skeletal muscle that occurs during or immediately after exercise".

Note that this definition applies to exercise-related cramps only, and therefore, it excludes a whole host of other possible cramps. We must point out that if you do suffer from very regular cramping, there are some conditions that can cause this - endocrinologic, neurologic, and vascular disorders, treatment with certain drugs, and occupational factors. Then of course, some cramps are what the experts call "idiopathic", which means they have no cause (but actually means we don't know what causes them, but it sounds better to say "idiopathic"!). If you are a regular cramper, it's probably worth seeing a doctor and just having an exam to determine whether any of these broad factors might be responsible.

But returning to muscle cramps, the lifetime prevalence of cramping is reported to be as high as 50%, which is remarkably high. Some people are also quite clearly more susceptible, and you can actually predict with a fair degree of accuracy who will cramp during a marathon based on their history and their racing strategies (more on this later).

The history of cramping - the electrolyte depletion theory

The earliest reports of muscle cramps come from 100 years ago, when labourers in hot and humid conditions of the mines and shipyards suffered from cramps. Even that far back, the sweat could be analysed, and it was noticed that the builders had a high chloride level in their sweat (chloride, incidentally, is one half of the salt in your sweat). The conclusion that was made was that the labourers were sweating out valuable electrolytes, causing their muscles (and nerves) to malfunction. The heat and humidity were key factors that caused this situation. It must be pointed out that no one prospectively measured the sweat of the labourers who DID NOT CRAMP, something that we'll look at in our next post.

Later, the builders of the Hoover Dam famously recovered from cramp when they were made to drink salty milk, entrenching the theory that salt loss was the cause of cramp.

And perhaps rather surprisingly, that was it - based on those anecdotal observations, the theory which you probably hold true today, was born. That is, cramp is caused by a loss of sodium, chloride, and later calcium and magnesium were added to the mix. Heat and high humidity were implicated as "accessories", and the term "Heat-Cramps" was even conceived. According to this theory (as seen by this article and the "expert" testimony) , cramps happen because athletes exercise in the heat, lose electrolytes in their sweat, and the depletion combined with high body temperatures cause muscle cramp.

For example, take these testimonies:

"When a young athlete experiences heat cramps, pull him or her off the field into a cool area and gently stretch the affected muscle. "Have them drink, drink, drink, and then drink more," says Albert C. Hergenroeder, professor of pediatrics at Baylor College of Medicine and chief of the sports medicine clinic at Texas Children's Hospital.

"High-sodium drinks will prevent children from getting heat cramps," says Jackie Berning, PhD, with the National Alliance for Youth Sports. "Gatorade has just enough sodium to prevent those cramps. But if you're a heavy sweater, and you're still getting cramps after drinking Gatorade, eat some salted pretzels or salted nuts. Those work fine.""

There is of course more to it than this, but the essence is that the serum electrolyte depletion theory was created without any controlled, clinical studies to establish whether the depletion of salt through excessive sweating was to blame. Rather, the theory was picked up on and used to spawn the numerous products you can purchase today. But, as I'm sure you've guessed, there are some holes in it.

The problems with the serum electrolyte depletion theory

First of all, there is a key conceptual problem here, and that is that when you sweat, you don't actually reduce electrolyte concentration. That is, there are certainly electrolytes in the sweat, but the concentration of these electrolytes is so low, that sweating is likely to make you HYPERTONIC, not hypotonic. We looked at this in our posts on fluid - when you sweat, you lose more water than electrolytes, because the sweat is HYPOTONIC. Therefore, sweating cannot lead to a fall in electrolyte concentration.

What transpired was that Gatorade (and the rest of the 'industry', it must be said) developed the theory of "salty sweaters", which is the term they gave to people who they said have abnormally high salt levels in their sweat. Small problem - no one actually knows what a salty sweater is. How much salt does there need to be in the sweat before you are placed in this group? No one knows. Recently, Professor Martin Schwellnus, widely published in this area, posed this question to scientists at the Gatorade Sports Science Institute at a conference on cramping - he received no answer.

The truth is, even the saltiest sweaters around still have hypotonic sweat, and so the more they sweat, the more they will cause their electrolyte levels to rise, not to decrease. This is a very obvious problem that is overlooked by the electrolyte replacement advocates.

Of course, those of you who read our fluid series might be thinking that if you then drink a lot of sports drink, you can reduce the electrolyte content, but that's yet another reason why drinking too much is not a good idea...

The cramping paradox - why specific muscles?

The second problem is something we asked you in yesterday's post. We asked whether the depletion of serum electrolytes would be expected to cause cramps in specific muscles, or all over? Hopefully it is evident that if a cramp was caused by a loss of serum electrolytes, there is no reason for the cramp to be limited to one muscle only. Rather, you would cramp everywhere. In fact, in people who have lost a great deal of salt and have become hyponatremic (not during exercise, but clinically), we know that they cramp in ALL their muscles.

But somewhat surprisingly, exercise-associated muscle cramps ONLY happen in the muscles that have been used extensively for exercise. The afore-mentioned Prof Schwellnus found in 2004 that the quadriceps, hamstrings and calves made up 95% of cramps in the 56km Two Oceans race in Cape Town.

Leading onto the next post - further evaluation of the electrolyte depletion theory

In the interest of time, we'll call it on this post for today, and say that in our next post, we'll tackle the electrolyte theory in more detail and look at some of the studies that have looked at people who cramp and those who don't and compare their values.

Join us then!

Further reading:

Schwellnus, M. (2007) Sports Medicine, vol 37, 2007

Schwellnus et al., British Journal of Sports Medicine, vol 37, 2004


Unknown said...

Great write-up Ross. As it's coming up to the hot part of the year here (plenty of outdoor training), it definitely has the wheels turning.

Unknown said...

The definition, "spasmodic, painful, involuntary contraction of the skeletal muscle that occurs during or immediately after exercise" seems a little vague to me.

For one thing, the Webster's definition of spasm is "an involuntary and abnormal muscular contraction". So we have a circular definition if we include the word "spasmodic".

But the thing I don't understand is, if it is an involuntary muscle contraction, why is it so painful? I don't have any medical background at all, but don't muscles expand and contract all the time when you run? Is it a freezing of the muscle in a contracted state that somehow causes pain? If so, what is the "somehow" that is causing the pain?


Anonymous said...

Interesting. I really like this blog. Two comments/questions though. I'd be curious if you agree with me or not.

First, you say that sweating increases electrolytes. Which, if you sweat and do not drink anything, is true. But I feel like you guys are not telling the whole truth, since most people drink some kind of liquid while exercising. So while I agree that sweating and not drinking will increase the relative concentration of your electrolytes, most people drink at least water during extensive endurance exercise. It's this pure water that ends up diluting your blood. So I think people still need to replenish their electrolytes after exercise. Gatoraid isn't necessary for sure, but at least some food or other nutrients are important.

Second thing is you then say that drinking a sports drink (like the hated gatoraid) will actually dilute your electrolytes (from the above mechanism). I don't know if I agree with this, since sports drinks have electrolytes in them. In theory they'll not only replace fluid but also replace those lost electrolytes. Any extra electrolytes taken in will just be excreted by the body. I don't know for sure, but I'd guess its impossible to get "water intoxication" from gatoraid since it shouldn't dilute your plasma.

robdbirch said...

I enjoy your site very much and it appears that the two of you are very passionate about your discipline. I would like to make the comment that at times it appears that the two of you are a bit overly critical about science from the market place, and particularly at one particular vendor, Gatorade. This is distracting from the science you are trying to get across. I would prefer to see the scientific data disputed from the free market scientist and not the voodoo science marketing concocted by their marketing organizations. I think the marketing aspect should be addressed and discussed, but If you would like to discuss the marketing I would suggest that these topics be put into a separate blog entry. Mixing the two is just plain distracting and creates a longer than necessary blog entry. I would like to see and understand where we are with the science of sport. I believe we're are all quiet smart enough to understand the shallowness of marketing. ;)

Thanks for the great blog!

Ross Tucker and Jonathan Dugas said...

Hello everyone

Thank you for the comments in response to the first post of the series. Always good to hear from people.

Stan, to address your comments, I can see where you are coming from. I will offer that the definition (which is the published scientific one, incidentally - I'll add that reference to the post, I didn't do it last night) is probably meant to convey that the muscle contraction is "Convulsive, jerky, and uncontrolled", rather than the "involuntary" part you picked up on. But I see the circular nature of it...

As for the pain, that's a good point. The only thing I can offer is that a cramp is a far more sustained, local contraction, nothing like what happens in cramp, where a very specific area of the muscle seizes up. So the lack of control and "synchronization" of contracting fibres (for want of a better word) is the cause of the pain. One of the more interesting things is that no one has really managed to measure the electrical activity in a muscle DURING a cramp. A couple years ago, we tried to do it at an IronMan triathlon, the theory being that a cramp would be measured as this massive spike in electrical activity, but the logistical difficult prevented our efforts...it's an ambition for the future.

But it's a really interesting question, I'll do a bit of background reading and research on it, and get back to you with a more appropriate answer. Hopefully by tomorrow!

For Ryan and Roger, we'll address those is separate replies!

Thanks again!

Ross Tucker and Jonathan Dugas said...

hello Robert

Thank you for your visit and for your comments. Yes, we are both very passionate about our fields.

Your point is taken on the marketing angle. I would have to argue, however, that when it comes to this particular issue, it's impossible not to dwell on the marketing if you wish to appreciate the science. Because in science (not sure whether you're involved in research), it's vital that you appreciate the paradigm of the person providing the information. We all have one, and I feel very strongly that people have not appreciated the motive behind the research on the fluids during exercise.

Because the paradigm is quite clearly that the science is part of the marketing of the drink. In fact, I would not be surprised to discover that the funding of scientific research is probably driven by the marketing budgets! Because when a company establishes it's very own Sports Science Institute, then you have massive potential for conflict of interests, and this is what has happened.

Now, added to this, one of us (Ross) has post-graduate level training in marketing and sponsorship, so it is a passion just as much as science is. But even without that, we both feel very strongly about how the science has been so corrupted by the money behind it, that we feel almost obliged to tackle the issue. Jonathan did an entire PhD immersed in the science issue, and it's obvious that the science is tainted by the marketing. So that certainly comes across in our posting on the topic.

Finally, you said that you believed "we're are all quiet smart enough to understand the shallowness of marketing. ;) "

I agree with you on that one, for the most part - I think we're lucky here in that we attract a very discerning and highly thoughtful reader base, for which we're very grateful. But I actually disagree that MOST people are smart enough. People DIE because of the advice they follow.

So when a guy with his PhD stands up and says "Drink, drink and drink more" as happened in that quote from this article (highlighted in maroon above), then who is going to argue? He quite clearly posseses the 'expertise', he has this qualification and so people listen. And they die, because drinking like he says can kill you.

So I don't believe that people are smart enough to see past the marketing, because they're not scientists. All they know is what they read in the magazines, the expert testimonials, the quotes from research, the brainy guys with the lab-coats who surely know better! And for this reason, we feel we HAVE TO tackle marketing very strongly. So while you are discerning enough to see past that, many people are not, and we're trying to cut through that clutter and get to the real point.

Lastly (apologies for the long reply), I will also put forward that because this post was the first in the series, it was always going to be a very broad overview and introduction to the concept. That meant that there would always be less of the science. It was the same with the fluid series - the first post was general, looking at a bit of everything, and then from the second post onwards, we tackled the science in far more detail. We plan to do the same with this one, and so in Post 2 and Post 3, I do promise that we'll really address the science in far more detail!

But the science and marketing have become so entangled that really, to address them separately would not make too much sense, I believe. It would be a "he said, she said" kind of argument, and so we try to put across why the other side (be it Gatorade, Pose Running, whoever) may be telling something different. If for example, a Gatorade or Pose advocate would like to debate this issue, then I would like them to tell everyone what my incentive is - I can certainly tell you theirs, and my argument is incomplete without it!

But thank you for reading and for your comments!


Anonymous said...

Very interesting. I would be grateful if you could provide the reference for the original study on the sweat of labourers that you discussed in the blog?

Ross Tucker and Jonathan Dugas said...

Hi Alan,

Thanks for reading The Science of Sport and for participating in this discussion.

The reference for that study is the following:

Talbott JH and Michelson J. "Heat cramps: a clinical and chemical study." Journal of Clinical Investigation. 1933, Volume 12, p 533-49.

This manuscript is freely available from PubMed Central:


Happy reading! (And please let us know if you have problems accessing the pdf)

Kind Regards,

Ross Tucker and Jonathan Dugas said...

Apologies, I already see a problem as the full link to PubMed Central has been cut off in that comment above.

Let's try this again. . .this time you must go to PubMed Central and navigate yourself to the Journal of Clinical Investigation archive:


Kind Regards,

Ross Tucker and Jonathan Dugas said...

Hi Ryan,

Thanks for the questions on all of the posts in this series.

Electrolyte losses and fluid
Drinking water to thirst will maintain the concentration of sodium in the blood. It is only when people drink to a "schedule," for example "x" mL per hour, and ignore their thirst, that they drink too much water and dilute their blood.

It is not necessary to ingest any electrolytes during exercise. Your body will maintain the levels (sodium is the biggest player) just fine by using the thirst mechanism.

There are rat studies from the literature that demonstrate this. In these studies the rats are dehydrated and then have equal access to water and a salt lick.

What these studies found is that first the rats drink water to restore any volume losses. . .and some hours later once they have restored their volume, they go for the salt. And in fact humans have a well developed sodium appetite, too, but seeing as how we far exceed our RDA for sodium on a regular basis, we rarely crave salt. The exception to this is when athletes crave salt, and all this represents is a normal physiological response.

Sports drinks will cause hyponatremia
Yes, sports drinks contain some sodium. However, in relation to the body fluids, they are what we call hypotonic, and that means they have less than the body fluids. Therefore adding sports drinks to the blood will only serve to dilute the blood.

It is entirely possible to get hyponatremia from sports drinks. This is an extremely important concept. The main reason is again that the sports drinks are hypotonic to the body fluids. There was a Gatorade-funded study that examined fluid ingestion in elderly people during 2.5 h of intermittent exercise. One day they drank water, the other they drank Gatorade.

The results were that in all the subjects the sodium levels started at about 142. They went down in both trials. Again, they decreased in both trials. In the Gatorade trial this fall was only very slightly different. In absolute terms it was perhaps one unit and it was not statistically different from the water trial. This fall was more pronounced in the women compared to the men.

Therefore when we look at these data, we show that in this population (elderly) ingesting water OR Gatorade to thirst causes a fall in sodium concentration from 142 down to 139-140.

In addition, in the 2002 Boston Marathon Cynthia Lucero died from hyponatremia that was caused by excessive ingestion of fluid---both Gatorade and water.

So, again, any fluid that is hypotonic to the body fluids will cause a decrease in the concentration. As a note, sodium the concentration of body fluids is about 140, Gatorade is 18, and water is 0.

I hope that helps, but please do keep the questions coming!

Kind Regards,

Anonymous said...

Thanks very much for the reference - the paper downloaded very easily and I look forward to reading it. My interest in the paper is as an exemplar of the potentially unfortunate consequences of "case only" studies. I do read your blog quite regularly and, as I mentioned in my request for the reference, find it very interesting. Thanks again.

Ross Tucker and Jonathan Dugas said...

Sure, it's only a pleasure Alan!

It is great to see our readers reaching for the scientific articles. If you can get past the jargon and understand the experimental design and protocols, then they are an excellent source of info.

Happy reading!

Kind Regards,

Tammy said...

When does the book come out? Sifting through the blog for reverse order "parts" is driving me to drink! But don't worry, I'm not drinking gatorade!!! :) Hope you guys are well.

Ross Tucker and Jonathan Dugas said...

Hi Tammy

Thanks for the comment! The book is in the works, I can assure you! Will let you know when we know, but there is so much information that putting it into a book seems logical and needed!!

Thanks for your "endurance" in working through the posts, and for all your comments! I don't know if we've ever said a proper thanks, but you're one of the more regular commenters, always with good suggestions and comments, so it's much appreciated!

We'll work on that book!


Anonymous said...

From what I have read, there is a roughly ten-fold range in the sodium concentration of sweat(200-2200 mg/L). Some people loose more salts than others. Moreover, there is a five to ten-fold range in the volume of liquid lost per hour. So there is small wonder that some athletes are affected more than others. Endurance athletes, I would guess, sweat less and loose less sodium, this added to their fitness carries them further.
When I cramp, I cramp systemically - more noticeable in the legs but it occurs all over.
The cramp is the inability to relax the muscle. That is, the inability to sequester calcium back into the sarcoplasmic reticulum in the muscle cell. This process is driven by ATP (energy status). I have often wondered if a lack of sodium stifles the co-transport of glucose in the gut causing general suppression of energy status and ultimately leading to cramps.

Unknown said...

This was very interesting. I ran across it only today, having done an internet search on the issue after cramping up over the weekend, and it has spawned a few questions / observations.

I have had bad cramps on a few occassions. They have always only occurred during very strenuous activity over extended periods of time in very hot weather (30+C). Extended periods means 5 to 7 hours at a heart rate of about 85% of max. The exercise I perform for this length in this weather is always cycling for me. I have noticed that the situation seems exacerbated if I have had a few beers the night before, or in the last case, took a flight from Europe to North America, and definitely did not drink enough on the flight. Extended exercise at lower temperatures has definitely not caused the same cramping effect.

In my case there does seem to be a link (although admittedly circumstancial - not scientific) between fluid loss and cramps. I realise that the loss of sweat will increase the concentration of electrolytes, but does the total volume/quantity of electrolytes in the body play any role? Is there any evidence that muscles need electrolytes to function properly in the first place?

I for one, can attest to the fact that Gatorade or similar sports drinks, in the above circumstances, do not help the situation very significantly. Overconsumption of sports drinks actually makes me feel ill and bloated. When I cycled by a Pharmacy during the 180km ride over the weekend that caused my cramping, I purchased oral rehydration salts which do seem to help after some time. If finished with not too much additional cramping, but I could feel that they were about to strike again at any time.

I also noticed a statement that the cramps only appear in the muscles / areas being used. While this statement is generally true at the onset of severe cramping problems, I can attest to the fact that severe cramping affects the entire body. While the cramping normally starts in the affected areas (I experience it first in calves or hamstrings), I have also got cramping in my abdominal muscles as well as the muscles around the diaphragm, and ribs and between the scapula as well as neck and other areas. These muscles are probably used in cycling, but nowhere near the use of the leg muscles. I think this is where the study of cramps during cycling might help. Often cyclists are a long distance from their origin and do not often have the option of stopping exercise or calling someone for a pickup. Sometimes you are on your own, and if you are doing a loop or "out and back" pretty much have to keep going to get back home (or to point of origin). This is where the next stages (cramping in other body parts) occurs, and is sometimes even more painful than the leg cramps. I have a cycling partner that I often ride with, and he also experienced similar cramping over the weekend (hamstrings and rib muscles). I have also seen other riders cramp up on long hot rides.

I exercise in our winter as well, with the same level of effort (cross-country skiing) and have never cramped. I ski for several hours every weekend and compete in a two-day 160km event which takes 7 to 8 hours per day at 85% heart rate to complete. I have never experienced a hint of cramp in winter - only in summer and only during extremely hot and strenuous conditions that left salt stains on my cycling helment and clothes. Whereas my fluid intake is also high in the winter, I seem to lose less fluid from sweat than fluid through breathing. I base this on my intake level (about 1 litre per hour or more) which is pretty consistent in winter or summer, the difference being the amount of sweat evidenced by the salt stains on my cycling clothing versus ski clothing.