Dehydration & Muscle Cramps: What Causes Them & How To Avoid Them

By Luke Bucci PhD, First Endurance Chief Scientific Officer

The most common complaint fielded about endurance training is cramping, known officially in scientific literature as Exercise-Associated Muscle Cramping (EAMC). This complaint is even more common than bonking, because the latter has an obvious cause and solution. EAMC, it turns out, doesn’t. We explain how First Endurance products use the latest scientific research and a refusal to accept axioms in product formulation in order to actually prevent dehydration cramps, not just treat them once they occur.

Challenging Assumptions

EAMC is sudden, painful muscle cramps during or right after exercise, and it can range from minor and annoying to extremely painful and debilitating. We’ve been taught to stretch, hydrate, and consume salt to prevent it, but observational and experiential evidence tells us that these practices can decrease cramping—but not as much as expected or hoped.

Despite common assumptions about preventing it, EAMC still happens regularly: 30-67% for American football, cycling, marathons, rugby, triathlons and just about every other long-term work and exercise (Troyer 2020). Because of this commonality among endurance exercises, the field of preventing cramps has suffered from complacency as to pursuing the cause and is instead focused on treating the cramps once they occur.

For those who just want the answer, it’s magnesium

By parsing scientific research and reviewing clinical studies related to both to EAMC and to various types of cramps and muscle spasms unrelated to exercise, I’ve identified a correlation between a specific electrolyte and actual prevention, not just treatment, of cramping and muscle spasms.

For those who just want the answer, it’s magnesium; for those who want to know more about the discovery process that led me to magnesium, I’ll begin with a background on the two predominant schools of thought—or “cramp camps”—related to the study of EAMC.

Fluid/Electrolyte Imbalance Theory

The predominantly assumed cause of EAMC is Fluid/Electrolyte Imbalance Theory (FEIT), which is what informs the hydration mixes we all consume while exercising. Viewed through the lens of FEIT, running out of water and sodium are the chief culprits of cramping because they are obvious.

This is accepted beyond athletics. Worker safety organizations, for example, advocate avoiding dehydration and taking salt for workers who sweat profusely in hot conditions—think coal miners and construction workers in the summer; however, they still get cramps in winter’s cold without sweating their way to imbalance. Likewise, many endurance athletes maintain proper hydration and salt intakes during exercise, but still have EAMC, usually right when they need to push at the finish and again despite preventing the fluid/electrolyte imbalance at the heart of FEIT.

Supplemental methods like eating bananas have also not provided complete solutions, and low levels of potassium and sodium at race endings don’t routinely correspond with instances of EAMC. Even salinized IV fluids administered before events to ensure proper levels haven’t been shown to prevent EAMCs any better than oral hydration or sports drinks.

So although FEIT helps many individuals and should definitely still be applied to endurance exercise, EAMCs are still prevalent. Don’t stop hydrating like you do now, but know that our current common practices to prevent cramping are far from perfect, as evidenced by the observational disparities detailed above and the second of the two dominant cramping theories, which I’ll discuss next.

Altered Neuromuscular Control Theory

These observational disparities started a new line of research called Altered Neuromuscular Control Theory (ANCT). The demon in ANCT is muscle fatigue sending signals to spinal cord neurons via normal nerve connections that in turn send mixed signals to contract, which leads to cramping by telling your muscle to contract and relax at the same time. Eventually, the fatigued muscle only sees contract commands, resulting in EAMC.

This isn’t the clear-cut cause of exercise-related cramping, though, as most of the scientific evidence informing ANCT is from carefully controlled lab settings in which electrical signals are applied to muscles to induce EAMC. Because cramping is unpredictable and because real-world athletes are bodies in motion, conducting research on ANCT in real-life settings is difficult and prevents thorough scientific rigor; however, ANCT has verified that stretching and massage is a valid way to treat muscle cramps, just not to prevent them. So far, ANCT research has not found a way to control neuromuscular connections to prevent cramps.

Who’s Right? Everyone!

There is a commonality between FEIT and ANCT theories for causing cramps: both are useful as components of a larger, comprehensive understanding of cramping during exercise. The culprit identified by both theories is nerve cells misfiring, which does explain why most EAMCs are in the most-used muscles (calf, lower leg, feet, hands, and forearms).

FEIT proponents argue that electrolyte shifts from interstitial to intravascular spaces make the nerve-muscle connection hyperexcitable, sparking misfires as unwanted contractions. It’s super difficult to study this process on a microscopic scale during real-life exercise, and it’s clear that just measuring whole-body sodium levels or sweat losses is not good enough to see that localized micro-difference.

The ANCT crowd looks at where those hyperexcitable signals go (spinal cord neurons) and see the problem there. The problem is there, but it’s also more local to the muscles, where the FEIT crowd sites it. The body is a system, and every link in the chain plays a role.

Looking Beyond Exercise

To better understand the situation, it’s useful to consider non-exercise cramp causes in other areas of the body for deeper insights to EAMC. Cramps (also called spasms) in blood vessel muscles can cause fatal constrictions in arteries. Contractions or spasms in uterine muscles prematurely before labor is another well-studied nerve-muscle cramping event. Interestingly, intravenous magnesium therapies have been used to treat both conditions with some—but not complete—success. Most of these persons exhibited low magnesium levels or poor magnesium intakes, so the level of success shows that a missing link between nerve-muscle connections leading to cramps may often be magnesium.

High-Level Field Testing

I’ve had success applying this theory in practice. During my Certified Clinical Nutritionist days, I saw ranked tennis players and race car drivers suffer from debilitating cramps even though they were getting enough water, salt, and food. After seeing case studies of magnesium preventing cramps in scientific literature, I recommended magnesium supplements, and after a few days to weeks the athletes did not have EAMC.

At the time I thought it must have been their individualities that were corrected to restore adequate magnesium status; it turns out it’s not so individual—more like a common, widespread magnesium intake deficiency that impedes normal nerve and muscle functions and increases cramping, even when other electrolytes like sodium and potassium are at healthy levels.

Magnesium & First Endurance

First Endurance has been using significant amounts of magnesium (along with sodium, chloride, potassium, and calcium) in EFS, EFS-PRO, and Liquid Shots from the beginning, and has received much feedback about reduced EAMC in endurance athletes.

Like anything else in the body, giving too much of anything—even something inherently beneficial like magnesium—can imbalance internal systems, resulting in abnormal functions that manifest as a null effect or even toxicity. That takes a LOT of magnesium, though—far more than products like hydration mixes provide, and the inclusion of all five electrolytes means First Endurance formulas further reduce the chance of any potential imbalance.

Once you’ve got a grasp of magnesium nutriture, physiology, and biochemistry, it’s easy to see how magnesium helps both muscles and nerves to prevent EAMCs, essentially checking the boxes of both theories of EAMC. But how to administer magnesium right isn’t easy or simple—fortunately, we’ve solved those issues with EFS, EFS-PRO, and Liquid Shots, and I’ll map the difficulties next.

OK, everyone is right. Now what?

Regardless of which side of the debate you fall on, there’s good news: Magnesium loss or redistribution from endurance exercise can explain both kinds of muscle cramps. There is evidence that magnesium during exercise is the best way to reduce muscle cramps, regardless of how they start, along with proper hydration and other electrolytes. We’ve seen it work too many times and there is a massive amount of support from a wide range of sports nutrition and magnesium research.

Scientists used to believe that taking additional sodium during exercise was the best way to keep cramps at bay. New research, however, shows you need the right amount and type of magnesium to stop nerves from causing muscles to misfire and prevent cramping.

Given the above, all we need to do is load up on magnesium before and during exercise and we’re good, right? Not so fast, nothing’s ever that simple in the human body. The solution to using magnesium to prevent EAMC lies in tying together that wide range of findings. To help do that, I’ve assembled a body of “weird facts” about magnesium that are gleaned from research and ultimately paint a broader picture of why both nerves and muscles need the right amount and kind of magnesium during long-term exercise to prevent cramping in a way that satisfies both theories of EAMC.

Weird Magnesium Facts

Weird Fact #1: More exercise means more ATP generation, which means more magnesium is needed. Why? As soon as ATP forms, the available magnesium stash (hanging out with taurine, actually) inside of cells is used to stabilize ATP when it is moved from its generation point to muscle contractile structures inside muscle cells. Magnesium needs to be shuttled back and forth inside of intracellular areas to keep your muscles contracting. Not to mention continuing to run and ramp up all those membrane receptors and enzymes. Some magnesium will get lost from its intracellular places in working muscles during long-term exercise. This is why magnesium uptake and maintenance is important for endurance athletics.

Weird Fact #2: Long-term exercise induces a sort of “spring tetany,” which is seen frequently in livestock and provides a clue that magnesium deficiency is a key primary contributor to misfires and cramping. This is also called “grass staggers,” “grass tetany” or “lactation tetany.” Tetany is muscle spasms (i.e., continuous cramps) from hypomagnesia (low serum/cellular magnesium). To quote one reference: “The tetany characteristic of hypomagnesemic disorders is the result of intracellular, cellular membrane, and extracellular metabolic effects of magnesium” (Goff, p.138). Meaning that the most-used muscles are the first ones to show cramps from not having enough intracellular magnesium in muscles. Sounds like EAMC, right?

The good news is that cramping and dehydration are easily preventable by making a few minor tweaks to your hydration strategy.

Weird Fact #3: The key to magnesium nutriture is not simply giving more – than can backfire and cause mineral imbalances. This immediately refutes most human clinical studies on magnesium, since they’re administering high doses of magnesium by itself, and those doses aren’t balanced with hydration and/or other electrolytes. That approach just begs for hit-or-miss science (mostly miss), and it explains why many magnesium studies do not find benefits for sports nutrition or human health – even when other evidence says they should.

Weird Fact #4: During long-term exercise (two hours or more), you are running primarily on your intracellular magnesium stash. Magnesium supplementation during exercise can maintain this stash IF the right amount and kind of magnesium is given, along with other electrolytes. Sodium (and chloride) is one prerequisite, along with a little – but not a lot – of potassium. Calcium, the counterpart to magnesium, is also a prerequisite. In other words, you need all the electrolytes for magnesium to have a chance to work during exercise. Deficits of any other electrolyte will imbalance magnesium, delaying uptake and thus, cell entry.

Weird Fact #5: It’s not easy for your body to get magnesium into the right cells at the right times. Or not even get past the gut. So how do we do magnesium right? Again, a deep understanding of magnesium helps figure it out. It’s really simple once you know what your body is really doing, and the answer is partially informed by facts 6 – 11.

Weird Fact #6: Magnesium does not have hormonal controls like calcium, sodium (chloride) and potassium. That means there is not a ready pool of magnesium in the body that can be quickly mobilized and sent where needed most. Instead, magnesium must be continuously ingested to keep feeding tissues. This was easy from traditional diets we evolved on, but not from a modern, magnesium-eviscerated diet. The corollary to this fact is that magnesium absorption into the gut is slow and metered, the weak link in the chain of magnesium status, which brings us to

Weird Fact #7: Magnesium absorption into the gut is tricky and unlike other electrolytes. Why? Each magnesium ion is actually surrounded by a shell of water molecules that are stripped off by specialized proteins in between intestinal cells (called claudins). This is the rate-limiting step for magnesium uptake into the gut lining cells. Kinda like a drip coffee maker instead of a coffee press. And you need to have the right kind of claudins specific for magnesium – another step ripe for monkey-wrenching. A diet adequate in magnesium (around 400 mg daily from foods and chelated supplements) builds up magnesium-specific claudins over time, but not all of us eat a diet adequate in magnesium. Another reason to use magnesium chelates that interchange with sodium chloride in the gut. This is why high doses of magnesium do not help raise intracellular magnesium – the uptake into the gut is spacetime-limited, and cannot be upregulated in a day or during a long-term event.

Weird Fact #8: Despite the limiting effect of claudins, having an adequate Vitamin D status helps magnesium absorption from the gut, but many athletes are not sufficient in vitamin D function, and the cycle time of vitamin D repletion is way too long for immediate help adding Vitamin D during exercise. Sunshine and daily intakes of 1000-5000 IU/day – that’s 25-125mcg using the new units for Supplement Facts panels – should be enough.

Weird Fact #9: Chloride also helps magnesium absorption in the gut. When consumed at intestinal pH levels, sodium chloride and some chelated magnesium forms (like dimagnesium malate) exchange magnesium for sodium to form magnesium chloride and sodium malate, both of which are rapidly absorbed. There’s no stomach acid needed for magnesium absorption from non-chelated sources like oxide, hydroxide, carbonate or some chelated forms. Other magnesium forms, especially magnesium oxide, cannot do this trick unless there is a lot of stomach acid, which is shut down during long-term exercise. Dimagnesium malate has human studies showing best possible uptake, and it also has a higher percentage of magnesium than other well-absorbed chelates like bisglycinate, making it the preferred choice for a magnesium chelate to use during exercise.

Weird Fact #10: Magnesium uptake from blood to cells is as tricky as into the gut – same issues. You need claudins and specific receptors to get magnesium from blood into cells. This is why blood levels of magnesium do not give accurate information on what is going on in the cells, misleading many researchers into disregarding magnesium supplementation. Human studies in endurance exercisers found it took weeks to months for supplemental magnesium to saturate intracellular magnesium (but they were using the wrong kind of magnesium without the correct balance of other electrolytes and factors explored here).

Weird Fact #11: Once magnesium is inside cells, keeping it there depends on having sufficient sodium, chloride, potassium and calcium, taurine, and a steady magnesium supply – further reinforcing the point that all five electrolytes are crucial to endurance athletics, not just sodium and potassium.

Weird Fact #12: The nervous system includes neurons zapping muscles with contract/relax signals, and those signals are carried by leg-length axons. Proportionally, that’s like us humans having one arm reaching coast-to-coast across America, giving sign language and registering feelings through touch. The scale is daunting, but every time we walk or run we prove it’s normal. This isn’t specifically related to magnesium, but it is a weird fact.

Weird Fact #13: We are not even going to get into the large literature on medical magnesium use for preventing and relieving life-threatening cramps in important arteries and uterine muscle/blood vessels. Long story short: intravenous, soluble magnesium works better than any oral form of magnesium, but is still not perfectly effective for these extreme medical conditions. Even iv magnesium has to deal with all the Weird Facts listed above. But this world-wide practice is effective enough to support all the Weird Facts about magnesium (#s 1 – 11).

The First Endurance Solution

All five electrolytes (calcium, magnesium, sodium, chloride, and potassium) are essential for cramp prevention.

Taken together, these findings explain why EFS & EFS-PRO supply plenty of each of the five electrolytes. Including all five helps your body sort out what it really wants and needs to prevent cramping, and then helps it get everything to the right places during exercise – inside cells, especially muscle and nerve cells. The answer, it turns out, is simple; it just requires looking beyond established sports nutrition practices (such as providing only sodium and maybe potassium) to find better, more effective solutions.

In closing, I should note that EFS and EFS-PRO provide a LOT of electrolytes, which may be a concern to some athletes. Fortunately, your body has efficient ways to dispose of excess dietary electrolytes – most notably via urine and sweat outputs during exercise. Over-consuming gives you the best chance to stay flush with electrolytes, supporting those muscles and nerves working the hardest to prevent muscle cramps, but doesn’t pose any risk in terms of actually taking too many electrolytes on board.


Goff, JP. Ruminant hypomagnesemic tetanies, Ch 35 in Current Veterinary Therapy – E-Book: Food Animal Practice, Anderson DE, Riggs DM, Eds., Saunders Elsevier, St. Louis, MO, 2008, pp. 137-40.

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