By: Peter Dobos and Molly Kenneth (nurse practitioner and medical crew for many TM, WTM, ironman, ultras, etc)

Have we got your attention? Good.

That title, despite sounding so dramatic, is absolutely not click-bait. People have been hospitalized as a result of over-hydrating, sometimes with life-threatening issues such as cerebral edema (your brain swelling) and pulmonary edema (fluid in the lungs) both of which are fatal if untreated. This is not something confined to ultra-marathoners who run for 6 days in the Sahara desert, or untrained couch-to-marathon over-reachers. This can and has happened in OCR.

We can bring this right to your collective front doors: A racer at the 24-hour World’s Toughest Mudder nearly became the 1st WTM fatality in 2016. This was a classic case of what is called Exercise-Associated Hyponatremia and was documented in detail by WTM medical crew member Margaret Kenneth FNP-C with help from Dr. Wesley Kerr MD-PhD. You can find it on Mud Run Guide here: A Personal Cautionary Tale from WTM 2016

With this current article, we hope to raise awareness of this condition, explain exactly what it is, what it does to you, how to treat it, and how to prevent it.

What is Exercise-Associated Hyponatremia?

Hyponatremia is the medical term low serum sodium and it is what most people mean when they say “electrolyte imbalance”. In plain language, exercise-associated hyponatremia (EAH) is an electrolyte imbalance in which the concentration of sodium in your blood drops below a certain level, and is specific to people engaged in long bouts of exercise, such as 8 or 24-hour obstacle course races. It is natural and expected to lose sodium during activity but only in extreme cases will you be aware of it.  

What causes it?

Fortunately, the main cause of EAH is well understood: you drink too much fluid, and the fluid that you drink has a lower electrolyte concentration than what is found in your blood. But it is the amount of fluid you drink that is by far the most important factor. EAH happens if you take in more fluid than you put out via sweating, breathing, and peeing. Other risk factors include exercising greater than four hours, inexperience/inadequate training, slow pace and being at the high or low end of the BMI chart.  

Since each body is different there is no formula for taking in X mgs of sodium to prevent the onset of EAH. Understanding that some degree of EAH is likely in your upcoming event and keeping several forms of supplemental sodium available to you at all times (chips, bacon, salt tabs, salt packs, pizza to name a few) is ideal.  It is ill-advised to eat salt to “stay ahead of” hyponatremia, the same way it is ill-advised to “stay ahead of” thirst by drinking copious amounts of fluid. Both scenarios are cases of “too much of a good thing”, and overdoing it on the sodium intake can actually cause you to swell, your blood pressure to rise and your heart to have to work harder.  

What are the signs and symptoms?

As with most challenges, recognizing the problem is the first problem. Some of the common early warning signs of EAH, such as lightheadedness, nausea, and dizziness can be confused with other exercise-associated conditions. However, there are two that seem to be unique to EAH: body weight gain and puffiness, specifically swelling of the hands and feet.

Body weight gain is tricky to track lap-by-lap, with the drastic changes in clothing and likely immersion in water weighing everything down. It could, however, be used as a possible diagnostic tool by medical staff if racers weighed-in just prior to the start. They could then be weighed again in the medical tent/facility if they are brought in or come in during the race.

Puffiness, especially in the feet, hands, and face, is the easiest ones for racers and crew to track in real-time. If you feel your fingers starting to feel “tight” and are starting to have a hard time making a closed fist because of “sausage fingers”, then it’s a pretty clear indication that you are experiencing mild EAH. Similarly, a pit crew can look for puffiness in the face, typically seen most easily around the eyes. Signs and symptoms of severe EAH include a headache, vomiting, altered mental status (confusion, agitation, delirium), seizure, and coma. These are shared with other possible conditions, but there are a few that stand out.


Overlap of EAH and Rhabdomyolysis:

Rhabdomyolysis is the presence of higher than normal amounts of broken down muscle cells in the bloodstream, often accompanied by muscle pain/weakness, cola-colored urine, and abdominal pain.  Left untreated this progresses to kidney failure because the broken muscle cells clog the kidneys’ fine filtration system the way hair clogs a drain.  Proper training will help, as will drinking to thirst. In this short article it is difficult to explain all the ways that EAH and rhabdo overlap, diverge, and potentiate the other but for our purposes here there is one thing you need to understand:  NSAIDs makes it all worse.

Do NOT Take Painkillers (NSAIDs)

These races almost always hurt, sometimes a lot, and for a long time. As a result, many ultra-endurance athletes take NSAIDs (Non-Steroidal Anti-Inflammatories) such as ibuprofen (Advil, Motrin), aspirin (Bayer, Bufferin, Ecotrin), or naproxen (Aleve, Anaprox) before, during, and after their race. DO NOT DO THIS.

The main reason to avoid it is that NSAIDs reduce blood flow to the kidneys which makes it more difficult to perform their blood cleaning function.  Add to the fact that you will have more broken muscle cell contents in your blood because of the intensity and duration of activity.  Rhabdo makes EAH worse because of the way that it limits your kidney's ability to clear toxins and release fluid.  As you become more toxic you are on the fast track to acute kidney injury and kidney failure.  NSAIDs make everything worse.  According to a recent Stanford study use of NSAIDs during an endurance event double the chances of acute kidney injury.  Untreated kidney failure leads to dialysis and death.  A moderate amount of acetaminophen (Tylenol) is ok provided you keep it below 3000mg/24 hours all sources.
Adding insult to injury is this: research has repeatedly shown that taking NSAIDs before and during an event DOES NOT IMPROVE PERFORMANCE AND PROVIDES NO PAIN RELIEF AT ALL. In multiple studies done with real athletes at real races, as well as in controlled lab settings, athlete performance and reported levels of pain or discomfort were exactly the same if they didn’t take the pills.


How Can I Prevent EAH?

The most effective prevention tool you have is to remember 3 simple words: drink to thirst. In other words, drink when you’re thirsty and stop when you’re not. Thirst is a very tried and true mechanism that has been around for hundreds of millions of years. It works.

The worst thing you can do is to go in with a plan to drink X amount of fluids per lap or per hour regardless of conditions or how you are feeling. Drinking to thirst has been tested and shown repeatedly to be the safest and most effective hydration strategy, both in races and in the lab.


How should it be treated?

You can likely treat the onset of mild EAH by simply being aware of any swelling, especially in your hands and feet. If your fingers start swelling up and feel tight and it starts getting hard to close your hands completely, then you are likely starting to exhibit early signs. Taking a salt tablet or two at this point will probably cause the swelling to diminish and disappear. Some ultra-endurance athletes use this as their hydration/electrolyte balance guide.  All early treatment is with oral intake of salty stuff; bouillon, chips, salt tabs, pizza accompanied by limiting intake of fluid.  

What you absolutely need to know is that many field medical services do not have the i-stat machine to run your chemistry panel and they choose to approach medical services in a bare-bones fashion with limited on-site care.  What this means to you is that the assessment of your EAH, rhabdo and kidney function will likely be entirely clinical judgment.  Which is fine because there is no reason to doubt professional opinion familiar with endurance medicine.  However, endurance medicine is unique and very different than street medicine and the use of contract ambulances at remote endurance events absolutely should concern you.  Treatment with normal saline is a death sentence in the EAH patient. When EAH and rhabdo appear in the same patient the low serum sodium level must be corrected before fluid resuscitation which means first Hypertonic 3% saline and only later normal 0.9% saline. 



After the event:  You must continue to take in fluids, salt and food as if you are still racing (yes, ribs, bacon, pizza and cake all come highly recommended).  Regardless of outward symptoms your kidneys have been to hell and back and how you care for them in the next 24 hours is crucial in determining whether you develop EAH or rhabdo.  Yes, you can walk off the course only to die in your hotel.  If you were on the road to EAH or rhabdo/kidney failure you can absolutely plummet yourself right into them by taking NSAIDs, drinking too much fluid, not eating.   Enlist the help of your friends and family, even if they aren’t with you.  Watch out for each other.  People have died alone in their hotel rooms following events that they performed quite well in too sick or stubborn to seek help.  

You can do this well and safely.  You just have to keep your wits and plan ahead.  You know how to run and lift and pull and press on.  Hopefully now you are better prepared to not just survive but thrive.  


Did you just pull this out of your butts?

No, we used the latest recommendations from the Third International Exercise-Associated Hyponatremia Consensus Development Conference, 2015 as well as the 2017 update to the aforementioned. The original documents are here if you would like to go straight to the sources:

Third International Exercise-Associated Hyponatremia Consensus Development Conference

Exercise-Associated Hyponatremia: 2017 Update



Lipman, G., Shea, K., Christensen, M., Phillips, C., Burns, P., Higbee, R., … Krabak, B. (2017). Ibuprofen Versus Placebo Effect on Acute Kidney Injury in Ultramarathons: A Randomised Control Trial. Emergency Medicine Journal. 34(10):637-642.

Miller, M. (2016, October 13). Clinical Manifestations and Diagnosis of Rhabdomyolysis. UpToDate. Retrieved from

Noakes, T. (2012). Waterlogged.  The Serious Problem of Overhydration in Endurance Sports. Champaign, IL: Human Kinetics.

Rosner, M. H., & Hew-Butler, T. (2016, January 13). Exercise Associated Hyponatremia. UpToDate. Retrieved from


Share this post!

Disclaimer: The viewpoints expressed by the authors do not necessarily reflect the opinions, viewpoints and official policies of Mud Run Guide LLC, or their staff. The comments posted on this Website are solely the opinions of the posters.