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The Salty Sweater – yet another Myth of Sports Science?

Since several months I had in mind to write about cramping, sweating and electrolyte/salt substitution. It is a topic widely promoted and rarely questioned. Electrolyte sports drinks and salt substitution concepts are based on the unproven assumption that there are athletes that lose especially high amounts of sodium, and that athletes lose more salt than fluid under extreme weather conditions. The web is full of recommendations based on sloppy arguments or lacking any scientific grounds. Before I introduce to you a different thought concept that seems to have much more logic to me than the electrolyte depletion model, I would like to present to you a simple calculation that gives clear-cut evidence of the fact that dehydration is not causing cramps. I quote Jonathan Dugas and Ross Tucker in their book “Runner’s Body”.

What is a salty sweater?

The sodium concentration of blood is 140 mM (this means that there are 3.2 grams of salt for every one liter of blood). Your sweat on the other hand has got a sodium concentration of 20 to 50 mM. This value varies widely between individuals (50 mM per liter sweat equals a loss of 1.1 grams of salt in every liter of sweat). A salty sweater is a person with a special high sodium concentration in their sweat. The exact amount was never defined, the term remains very vague until today. Let’s assume that salty sweaters have 100mM of sodium in their sweat. As a matter of fact these guys would lose 2.3 grams of sodium in each liter of sweat. However, as the plasma concentration is 140 mM (3.2 grams per liter), even a salty sweater will experience an increase in blood sodium during heavy sweating, because more fluid is lost than sodium, relative to plasma.

So, apart from the fact that no one really knows what a salty sweater is, even the saltiest of sweaters has still got a hypotonic sweat. The more they sweat the more their electrolyte levels rise.

Does dehydration cause cramps?

Sports drinks cannot help to replenish the lost sodium, because they are hypotonic as well and only dilute the plasma further. If you go through the available data, data that is never questioned, then you don’t find any hard-wired proof for the dehydration-electrolyte theory for cramping. There is obviously no explanation for how an athlete with normal electrolyte concentration and less fluid loss can experience cramps. Many athletes swear by electrolyte gels or salt tablets as cramping-preventing agents. The data from the field studies don’t support this effect, since crampers and non-crampers have similar electrolyte levels. For every athlete who finds that electrolyte supplements work, there are probably five who take them and cramp anyway. No study has ever shown there effectiveness, and even the ancedotal evidence is quite week.

Fatigue is a key component in the muscle cramp story

This hypthesis was first raised by Martin Schwellnus in 1997. He found no association between electrolyte levels and cramp risk in runners and Ironman triathletes. He suggested a theory that accuses fatigue being the main culprit for cramping. Muscle cramps are thus the result of a dysfunctional reflex control of the motor nerve.
We are talking here about exercise-induced muscle cramps, and this is important to stress because cramps that are due to an electrolyte imbalance may occur generalized as it is the case in hyponatremia. The main target of cramps are the active muscles quads, calves and hamstring. This indicates that cramps are associated with the process of muscle contraction. Studies have found that racing on a course that is hillier than an athlete’s normal training grounds and racing above a level of training that can be comfortably handled are predictive factors for muscle cramps.
People who cramp are invariably racing harder or starting a race at a pace faster than their training has prepared them to do. Training is rarely an occasion where cramping occurs, it is the races and it is often the end of the race… All these observations are pointing to fatigue and muscle reflex control being involved in muscle cramps.

What is the most effective treatment for exercise-induced cramps?

Easy! Everybody knows it. It is stretching, passive stretching or quitting the race. Regular stretching may help reduce the incidence of cramping. It is effective because it reduces the alpha motor neuron activity. You should dare to stretch before cramping starts, even during a race, especially, if you know that you are prone to cramps.  It seems to be obvious that fatigue weakens control mechanisms,  that otherwise avoid neurons to fire relentlessly, bombarding the muscle giving it no chance to relax.  Conclusively, one could say that exercise-induced cramps are a phenomenon associated with fatigue, and fatigue giving way to neural activity, muscle excitation and relaxation going astray.
Evidence for the fatigue model is strong, but studies are still to sparse to make it a generally accepted hypothesis. Nevertheless it should give you some reason to reconsider your approach to cramping and raise some doubts concerning the dehydration-electrolyte model. In the end this story shows that the body is a complex organism, and that the fatigue model may turn out to be as incomplete as the dehydration-electrolyte model seems to be wrong.

In my next blog post I shall go a little bit more into the details of muscle excitation and relaxation process.

Susann

Susann

Susann is the biest prototype and head of the team. She is Austrian, has studied medicine, meaning she is a medical doctor and the Biesters' alpha wolf. Susann continuously produces new ideas, is strong in making concepts and is practically always ON FIRE. Without her BIESTMILCH wouldn't be where and what it is today, and anyway - not possible.

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10 Comments

  1. This original article also focuses on ‘fatigue’ as opposed to hydration status. Dehydration to -3% did not affect cramp threshold.

    Med Sci Sports Exerc. 2010 Mar 25. [Epub ahead of print]
    Three Percent Hypohydration Does Not Affect the Threshold Frequency of Electrically-Induced Cramps.
    Miller KC, Mack GW, Knight KL, Hopkins JT, Draper DO, Fields PJ, Hunter I.

    1North Dakota State University, Department of Health, Nutrition, and Exercise Sciences, Fargo, ND, USA; Brigham Young University, Departments of Exercise Sciences2 and Statistics,3 Provo, UT, USA.
    Abstract
    PURPOSE:: Dehydration is hypothesized to cause exercise-associated muscle cramps (EAMC). The theory states that dehydration contracts the interstitial space thereby increasing the pressure on nerve terminals and cramps ensue. Research supporting this theory is often observational and fatigue is rarely controlled. Inducing cramps with electrical stimulation minimizes many of the confounding factors associated with exercise-induced cramps (eg, fatigue, metabolites). Thus, our goal was to minimize fatigue and determine if hypohydration decreases the electrical stimuli required to elicit cramping (termed “threshold frequency”). METHODS:: Ten males cycled for 30 min bouts with their nondominant leg at 41 degrees C and 15% relative humidity until they lost ~3% of their body mass (~2 h). Dominant leg flexor hallucis brevis muscle cramps were induced pre and posthypohydration and threshold frequency was recorded. Plasma osmolality (OSMp) characterized hydration status. Total sweat electrolytes (Na, K, Mg, and Ca) lost during exercise was calculated. Subjects repeated the protocol 1 week later. RESULTS:: Subjects were hypohydrated postexercise (preexercise OSMp= 282.5 +/- 0.7 mOsm*kg H2O, postexercise OSMp=295.1+/-1.1 mOsm*kg H2O, P<0.001). Subjects lost 3.0+/-0.1% of their body mass, 144.9+/-9.8 mmol of Na, 11.2+/-0.4 mmol of K, 3.3+/-0.3 mmol of Mg, and 3.1+/-0.1 mmol of Ca. Mild hypohydration with minimal neuromuscular fatigue did not affect threshold frequency (euhydrated=23.7+/-1.5 Hz, hypohydrated=21.3+/-1.4 Hz; F1,9=2.81, P=0.12). CONCLUSIONS:: Mild hypohydration with minimal neuromuscular fatigue does not appear to predispose individuals to cramping. Thus, cramps may be more associated with neuromuscular fatigue than dehydration/electrolyte losses. Health care professionals may have more success preventing EAMC by focusing on strategies which minimize neuromuscular fatigue rather than dehydration. However, the effect of greater fluid losses on cramp threshold frequency is unknown and merits further research.

  2. Hi,

    Thanks for the interesting article. I have been participating in triathlon and coaching for 20 years and thought I would share my thoughts.

    I do very much agree with this article that the main cause of cramping is muscle fatigue. However, it would be interesting to see the correlation to incremental blood viscosity as a person dehydrates, and the additional increase in actual energy required to maintain a pace. Please take it on I am not a scientist and have no medical background, also have no ties to any ‘sports products’.

    My logic is, although the electrolyte drink does not directly affect cramping as per the research, I believe there is clear evidence that increase water consumption (electrolyte drinks) decreases dehydration, which maintains blood viscosity. Thus, if a person does incrementally dehydrate over the duration of an event, the blood thickens and their efficiencies become worse. This in turn means a a larger per use muscle contraction per stroke or step to achieve the same wattage output. Thus, cramping can be indirectly related to and caused by in sufficient electrolyte (or water) consumption.

    At the end of the day, I recommend to clients – you have put in hundreds of hours training for a major event, whether it works or not the cost of an electrolyte drink is small and if it assists either on a physical level or mental level, then why not?

    I would be interested in thoughts.

  3. Scott, thx for your comment. I need a little time for answering to your comment in some detail. I am currently on a job at 70.3 in New Orleans… getting back to you next week the latest, kindest regards, susann

  4. so you agree that as i workout i lose salt, but somehow the amount of salt that remains in my blood stays the same? where does that extra salt come from?

    if i drink water during a workout, while i sweat the whole time, aren’t i diluting my blood? don’t i need salt replenished? if yes then why wouldn’t i want to have a drink with some salt in it? sorry but i’m confused. this article doesn’t make sense to me.

  5. Hi Frank,

    sorry for confusing you Frank, but the body is a complex and difficult machine to understand. We yet know comparatively little about all the various regulation processes that keep the balance of the body and thus make life possible.
    You lose salt, but the salt you lose by sweating is not just a simple equation where out equals in… hormones are regulating the water and electrolyte household to keep it stable even under extreme conditions. The pH variations of the blood are minimal, because changes are life-threatening.
    There are centers in the brain that control and regulate the levels of electrolytes and water, even if you sweat a lot, there are other fluid compartment (e.g. guts) where salt is available. The body does not rely on substitution only but keeps its salt content stable by recirculation (e.g re-absorption in the kidneys). And moreover, you may not forget that nutrition and plain water all contain salts.

    Water and salt regulation can be disturbed in situations of severe stress, and then the regulatory properties of the body are weakened. Normally, the body knows how to handle these problems and a special substitution of salt is not required. This of course cannot be generalized. Different situations of severe stress and dysregulation may need support like an extra amount of electrolytes. What some of the studies say is that it is not an easy calculation in which you measure your salt and water losses and simply substitute them.

    I hope I did not add more confusion to the equation, cheers susann

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