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Monday, November 26, 2007

Muscle Cramps: Part IV

An explanation of the evolution of science

Over the past week, we've taken what has turned out to be a pretty intense look at muscle cramps. We began with a discussion of how muscle cramps were first attributed to a low serum electrolyte concentration, without any substantial evidence for this theory. We then moved on to show that, in fact, people who cramped have the SAME electrolyte concentrations and levels of dehydration as those who do not cramp - this is pretty strongly suggestive that cramping is not caused by either dehydration or electrolyte depletion. Then on Saturday, we described a new model for muscle cramps, involving a 'malfunction' in the reflex control of muscles during fatigue.

This series, more than any other we've written so far, has stimulated some telling comments and incisive questions. And we're very pleased with that - our intention here at the Science of Sport was always to stimualte discussion and debate, and we pride ourselves on the thoughtful and discerning readership we clearly have.

In fact, we want to be challenged - we invite the sceptics and the doubters, because it's only through that type of discussion that we ALL work towards the truth! We put the evidence out there in what we believe is the most objective way possible. If that evidence is challenged, we enjoy the discussion, provided it's thoughtful and relevant! Of course, this creates a time-problem for us, because we can't respond adequately to all the excellent questions we receive. So the day is coming where we'll have to pass on responding to some of your comments and questions, unfortunately. For now, we do our best, but please bear with us if we can't turn around all the questions in the time we'd like to.

However, what we would like to do today is to return to one particular issue which has come up again and again since we began this series - this is the issue of low electrolyte levels: Are they caused by loss of electrolytes in sweat?

A brief overview of the evolution of knowledge - science is like watching chess, one square at a time

Before we get stuck into the actual question, I have to just step back and give a brief overview of how science evolves. I heard this analogy from a famous physicist named Richard Feynman - he of the Challenger explosion, and maybe the world's most famous scientist in the 1980's. It's the best analogy for science that I've heard.

Feynman said that science and research is like trying to understand the game of chess by watching just one square on the chess board! You watch that single square and based on observations, you create a series of hypotheses. So for example, your first hypothesis will be:

All pawns move in a straight line and cannot move backwards or diagonally.
However, the more you watch, the more you measure, the more you add to your understanding. And eventually, there comes a point at which your initial hypothesis is disproved! For example, you suddenly notice that pawns can in fact move diagonally, if they are capturing an opponent's piece! Your initial hypothesis must now be revised, or it will be incorrect.

As you go, you develop further - soon you discover a new piece - a bishop, which is only able to move diagonally. You also realise that a rook (or castle) can move in any direction except diagonally! And later still, you might discover that another piece, the queen, can move in any direction, forward or backwards!

This is a wonderful analogy, because it shows three key aspects of research and science:
  1. You can never see the whole board - in science, you are always looking at one piece of the bigger picture, and trying to make inferences from your observations and measurements. This has implications for how one can apply data to other areas - just because a pawn moves forward in my square doesn't mean it can't move diagonally somewhere else!
  2. You have to constantly re-adjust your hypotheses based on new observations. In otherwords,as you learn, you discover that what you once thought is only partly correct, or sometimes, completely incorrect!
  3. Finally, and most importantly, when you make an observation that challenges your existing hypothesis, YOU MUST CHANGE THE HYPOTHESIS. Failing to do so means that you are incorrect!
For example, let's say that your initial hypothesis is that pawns only move in one direction. If you suddenly observe that they can move diagonally, you would be incorrect if you held to the theory that they move in one direction only! Your understanding of the game would be flawed as a result of your failure to reassess and change your hypothesis!

And that brings us to the issue of electrolytes and sweating, and how they relate to muscle cramp.

The issue - can your electrolyte concentration fall as a result of sweating?

In the interests of time (your time reading this, and mine writing it!), we are going to leave the application of this important question over until tomorrow, when we'll throw some examples out there and prove that sweating does NOT cause low electrolyte concentrations.

For today, we end off with a few questions, to stimulate thought ahead of that post, which we hope proves once and for all that low sodium levels (hyponatremia) and cramping are not caused by loss of salt in the sweat:

  • First, a basic model - you have 10 cups of water, and 10 spoons of salt. If you mix all these together in a large container, then you have a salt concentration of 1 spoon of salt per 1 cup of water (C = 1)
  • Now, if you wish to somehow lower the salt concentration of that mixture, there are two ways to achieve this:
  1. You can pour in more water, or
  2. You can remove some of the salt
  • Now, let's assume that you are losing BOTH water and salt from the container. If you lose them in equal amounts, the salt concentration stays the same - for example, take out one cup of water, and one spoon of salt - you now have 9 cups water and 9 spoons of salt - the concentration is STILL 1 spoon/cup.
  • But, if you lost relatively MORE WATER THAN SALT, then your concentration would go UP. For example, you lose 5 cups of water, but only 1 spoon of salt. Your new concentration is 9 spoons of salt in 5 cups of water = 1.8 spoons per cup! A similar thing happens if you lose more salt than water, except in this case, the concentration will fall.
  • So the next question, which I'm sure you're already asking yourself - when you sweat, do you lose more salt than water? Or is it the other way around, with more water lost than salt?
The answer, which our regular readers will know since we've emphasized it previously, is that sweat is HYPOTONIC, which means that it has a relatively lower salt concentration than the plasma. Therefore, we're dealing with a situation where sweating would cause...an INCREASE in the body's salt concentration!

We'll tackle this issue in tomorrow's post, where we'll throw some real physiological values out (as opposed to simple cups of water and spoons of salt!), and show that low electrolyte levels, and hence cramping, cannot be caused by sodium loss in the sweat!

It's all part of looking at the chess board, and changing the hypothesis!



Nancy Toby said...

I hope you include some information concerning *intracellular* electrolyte concentrations, since this is the effective site of the muscle cramp - and it's the piece of the chess board that one needs to fully understand in order to formulate a defensible hypothesis concerning the etiology of muscle cramps.

Anonymous said...

I always thought it was a lower potassium concentration in the blood that caused cramps, not necessarily lower electrolyte concentrations. You havent convinced me of your new theory yet because you have only focused on sodium.

Ross Tucker and Jonathan Dugas said...

Hi Anonymous, and thanks for the very relevant question about potassium concentrations.

First we should say that potassium is an electrolyte---as is sodium, magnesium, chloride, and any other particle with either a positive or negative charge.

You are correct in that low potassium concentrations are purported to be a cause of cramps---how many of us can recall being told to eat bananas during summer soccer games as kids?

However, potassium losses via the sweat are even lower than sodium losses. Whereas sweat sodium concentrations are in the range of 20-60 per Liter, potassium concentrations are 8-10 per Liter.

Therefore we are losing even less potassium via the sweat than sodium. However, as we have tried to explain, sweating will cause the concentrations of electrolytes only to rise, not fall. This is because although sweat contains some things like sodium and potassium, it is still mostly water, and therefore we are changing the volume of the extra-cellular fluid more than we are changing anything else.

The net result is that as the volume decreases the concentration(s) increases.

I hope that makes sense, and thanks again for participating in this discussion!

Kind Regards,

Anonymous said...

You wrote that potassium in sweat is around "8-10 per liter." But according to MedLine Plus, the normal blood concentration is 3.7 to 5.2 mEq/L for potassium (135 to 145 mEq/L for sodium). So does this mean that potassium levels are indeed dropping from sweating, even as sodium concentration rises? It still wouldn't explain why cramps are localized but might be a contributing factor.

Anonymous said...

Hi Guys

It's addictive to wanting to know the truth and the truth shall set us free.

Pysiologically it makes sense to say that excessive sweating increase salt concentration in the body. This is one side of the coin.

It's a known fact that the salt concentration in the body can be diluted by drinking too much water to the extent of causing hypotremia.

So in the prolonged run which surely cause excessive sweating, is it not true that water replenishment only can dilute the original contents of electrolytes if water intake is more than water loss due to sweating?

Ross Tucker and Jonathan Dugas said...

Hi Clyde, and thanks for adding that info from Medline.

The serum potassium concentrations are very tightly regulated because when this value falls and produces what is known as hypokalemia, the individual's risk of serious heart arrythmias rises substantially.

The first reference I checked stated 8-10, but upon further scratching around it seems the range is a bit wider--more like 1-10.

But we do not often see clinically significant changes in serum potassium associated with endurance exercise. In fact if we look at the Sulzer et al study from the Ironman both groups had post-race potassium concentrations of 4.2-4.4, which are right in the middle of the normal range.

However the real story with potassium is that during exercise it initially rises a bit (in proportion to the amount of contracting muscle mass) and then is taken up by inactive muscles during exercise, the result of which is that it remains fairly constant during endurance exercise due to relatively small amounts of active muscle.

The excellent review article (although you might need institutional access to download it) is:

Lindinger MI. "Potassium Regulation During Exercise and Recovery in Humans: Implications for Skeletal and Cardiac Muscle." Journal of Molecular and Cellular Cardiology. 1995. Vol 27, p1011-1022.

I hope that clarifies the potassium story a bit more, but please keep the questions coming if needed.

Kind Regards,

Ross Tucker and Jonathan Dugas said...

Hi Half-timer, and thanks for chiming in here!

Indeed, if you were to replace 100% of your weight losses with water, you would be diluting the plasma sodium concentration.

However, the thirst mechanism does not work like this. If you browse over to our series on dehydration, in Part IV we tried to explain the physiology of thirst. In short, the concentration rises, this causes you to be thirsty, and you ingest a bit of water to bring it back down.

The very important point is that body weight is not regulated. Instead, the concentration of the plasma is regulated and one insignificant consequence of that is that the body weight falls a bit.

So your thirst mechanism does not stimulate you to ingest 100% of your weight losses, and instead we replace only about 50-60% of these losses. . .which is entirely ok because again, weight is not being regulated. What happens is that when you drink water to thirst you maintain your plasma osmolality (concentration) just fine, and do not dilute it.

On a side note, endurance exercise even in hot environments does not produce "excessive" sweating, as the sweating response is required to help cool the body. Therefore the higher the metabolic rate, the higher your heat production, and the more sweat you produce to cool yourself---there is nothing "excessive" about it and instead it is necessary and entirely appropriate.

Will sweating larger volumes mean you get thirsty more often? Absolutely, and that will stimulate you to ingest more fluid, but again you will replace 50-60% of your weight losses and maintain your plasma osmolality.

Thanks again for participating in this discussion!

Kind Regards,

Ross Tucker and Jonathan Dugas said...

Dear Anonymous

Thank you for the comments on Potassium - have a look at Part 2 of this series, because there, we DID in fact look at postassium levels in crampers and non-crampers, and showed the results suggesting that the levels of potassium were NOT DIFFERENT between the two groups.

This finding, combined with the theory Jonathan has presented to you in the earlier answer, suggest that the same goes for potassium as for sodium - they don't cause cramp.


Tammy said...

Any theories on prevention? The only comment I saw regarding possible cause was in regards to over-pacing. I have an athlete who has done a one-day 205-mi bike ride two years in a row. Both years, severe hamstring cramp at about the same time. He still managed to push through, but it would be nice to figure out how to prevent this in the future. BTW, without advising me, he drank FIVE GALLONS of Gatorade Endurance and didn't have to pee once! 95+F weather, and almost 12 hours of ride time. Whew! Thanks guys... love the content.

Newuro said...

I just recently discover this excellent blog on cramps. I am a physician and I have been running since 2003 and lately doing triathlons (2 IM, 3 70.3, Olympic and Sprints) since 2006. I suffer from severe inner thighs cramps (almost 100% of the times the left leg). Once a cramp occurs my day is almost over.
The most frustrating part is during swimming. I could swim ~1500-2000 mts w/o too much struggle but beyond that, it will be hell for me. I have tried not kicking but it doesn't matter, cramps will always show. I have been able to complete the two IM's thanks to the wetsuit which help me a lot, in terms of flotation but more for the support to the thighs. The muscle tightness or cramps are to the point that it is always a struggle to get out of the pool.

I agree with you in that there is more than hydration and electrolytes as the etiologic factor. My father and 12 y/o daughter suffer of night cramps, so I think there is a hereditary neuro-muscular disorder. After a hard or long workout I will cramp while resting or during the night. I have tried to drink as much as possible (water and supplements like Perpetuem by Hammer Nutrition), take Sport Legs before and Endurolytes every hour, along with 1 gel/hr (100 cal/hr). I have drink Club Soda (due to its content of quinine) the night before a long run or long ride. Pickels, TUMS, etc, you named it ! But still have the cramps.
I have run three full marathon and cramps appear between mile 20-23.
I agree with your theory of muscle fatigue and continuous firing of the afferent fibers, but any words of wisdom about how to avoid them. Just recently I discovered how to stretch to relieve the inner thigh cramp, but again once the cramp occur it will be a struggle to finnish the run or ride.
I apologize for such a long posting (been my first) but this is the first time I found some sound information about the kind of cramps I suffer. I will appreciate any comments.

Newuro said...

are there any labs test or physiologic studies available for the frequent crampers ? I and more than willing to participate in any study which could show light !