Myth #2: Muscle cramps are caused by electrolyte depletion
Before we get into the logic behind this belief, it is important to understand where it came from. According to this article from Sports Scientists, the theory of electrolyte depletion and muscle cramps dates back more than 100 years, to laborers who worked in hot and humid mines and shipyards. Even as far back as a century ago it was possible to analyze sweat. When researchers tested the laborers who were cramping, they found that they had lost a significant amount of chloride (which is one half of the salt in your sweat). Based on this evidence, the researchers concluded that chloride lost must be responsible for the laborers’ cramps. However, it is important to note that the researchers did not test the workers who didn’t cramp.
Later, in the 1930’s, builders at the Hoover Dam appeared to be aided in cramp recovery by drinking salty milk. Interestingly, this event is also cited by Gatorade as “evidence” to support the efficacy of its formula (we will look more into Gatorade’s Sports Science Lab in an upcoming post). Through these two anecdotal observations, the electrolyte depletion theory was born and “verified”. Just as with the dehydration theory, however, modern researchers are taking issue with it.
First, let’s pose a question. If the electrolyte theory is correct (or the dehydration theory for that matter), then shouldn’t every muscle be equally likely to cramp? After all, we sweat and lose electrolytes throughout our entire body - not just the muscles that are doing the work.
Dr. Martin Schwellnus, who we discussed in Part I of this series, had the same question. In his 2004 study of runners at the Two Oceans Marathon, he found that 95% of muscle cramps occurred in runners’ quadriceps, hamstrings, and calves. These cramps essentially struck only in the muscles that had been used extensively and for long periods of time.
In addition to observing where the muscle cramps occurred, Dr. Schwellnus and his team also measured the athletes’ electrolyte levels: sodium, potassium, and magnesium. The results are shown in this table:
If you recall Part I of this series, you will remember that the “crampers” were more hydrated than the non-crampers. And, as the chart indicates, the “crampers” had higher sodium levels than the non-crampers. In addition, the crampers had higher levels of magnesium.
So what does this all mean? If it is true that sweating leads to dehydration and electrolyte depletion, then we would expect those who cramp to have less fluid in their body, as well as fewer minerals. What we found is the opposite. The athletes who cramped were more hydrated and had a higher concentration of both potassium and magnesium.
Last, we will turn to a 2005 study, performed at the University of Alabama, published in the Journal of Athletic Training. 13 college-aged men with a history of calf cramps were asked to perform a rigorous regimen of exercises, designed to fatigue the calf muscles. The regimen was performed on two separate days, in hot and humid conditions. On one day, the participants were given sports drinks with extra salt added in. On the other day they were not allowed to drink any fluids.
7 of the participants experienced muscle cramps when they were not given any fluids. When the salty sports drink was consumed, 9 of the participants experienced cramping, although some of the men were able to exercise longer than the no-liquid trial. Although it is tempting to conclude that the electrolyte-filled sports drink delayed cramping, the researchers concluded that other factors must have been at work, “It appears that dehydration and electrolyte loss are not the sole causes of EAMCs [exercise-associated muscle cramps], because 69% of the subjects experienced EAMCs when they were hydrated and supplemented with electrolytes.”