Posted on 21 Jun 2009 18:24
Part IV (Theories and Fallacies of Muscle Cramps)
BY Ross Tucker, PhD and Jonathan Dugas, PhD
The Science of Sport
Over the past three articles, 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 in Part III, 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 next time, 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 article, 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 the next article, 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!
Used with permission. All rights reserved by the authors.
This page created 21 Jun 2009 18:24
Last updated 27 Feb 2016 21:54