By Sam Healey

Role of Electrolyte and Fluid Balance During Endurance Activities

Managing your body’s fluid and electrolyte balance is the top priority of any participant in an endurance race. If a competitor doesn’t manage this successfully then a range of medical conditions and illnesses can occur on a scale that begins at feeling a bit nauseous or getting muscle cramps and ends at the potentially life-threatening conditions of dehydration and hyponatremia.

The bulk of research into this area previously focussed very much on marathon runners as this was the fastest growing “endurance” sport. Thankfully, because of the growth in ultra-marathons and Ironman particularly in the United States, the past few years have seen far more studies on electrolyte and fluid balance for much longer endurance activities.

What are electrolytes and what do they do?

Electrolytes (or salts) are essential for the proper function of cells and organs. Chemically they are minerals that become ions in solution and acquire the capacity to conduct electricity. There is a whole panel of minerals necessary including sodium, potassium, magnesium, zinc, calcium and chromium, etc.

Electrolytes help nutrients move into the body's cells and help wastes move out. They also aid in the stabilization of the body's pH level. Electrolytes can affect your heart rhythm, your muscles’ ability to contract, your brain function and energy level.

How do they become unbalanced during endurance activities and why is that a problem?

There are three main ways that electrolytes become unbalanced during long periods of physical exertion and they are all magnified if you are exercising in a hotter climate than you are used to.

1. Loss of salts through sweat, especially sodium.

2. Deficiency of fluid in the body due to not drinking enough fluids.

3. Dilution of electrolytes (especially sodium) through excessive fluid intake.

An imbalance in electrolytes can ultimately lead to two illnesses; either Hyponatremia, in which the sodium concentration in the blood serum is lower than normal, or Hypernatremia, (often and less accurately referred to as dehydration), defined as an excess of sodium in the blood serum, and which occurs normally due to a deficit of free water in the body rather than to an excessive intake of extra sodium.

Hypernatremia Hyponatremia
You can also read about dehydration here to understand the differences.

How do I keep the balance when I’m racing?

Just drinking water when you sweat is not the solution to avoiding dehydration and hyponatremia, and this is the basis for the multi-billion dollar sports drink industry that has exploded in the last couple of decades.

Make sure your electrolyte supplement contains the full spectrum of electrolytes.

Do not wait until you start getting cramps as the indicator that you need to replenish electrolytes.

Planned and regular intake across the exercise period is advised. Do not overload the body with electrolytes. You are aiming to maintain and at best optimize normal body function not stress it with a surfeit of chemicals.

Drink the amount of water that is appropriate for the climate and your pace, sweat-rate, and own physiology.

What do I need to consider when I’m taking part in an endurance race?

As you can see from the list of causes above, and as many competitors have experienced in races, unless you are clear about the amounts of water and electrolytes you are taking in, and the amount of salts and fluids you are losing from your body, it can be difficult to work out which set of conditions is making you feel ill at the time.

This issue is compounded by the fact that the symptoms of various heat illnesses and electrolyte imbalances are, at the early stages, pretty similar: nausea, headaches, lack of energy, lightheadedness, cramps, diarrhea, vomiting etc.

There is more and more advice being generated about this topic online, not least by the manufacturers of electrolyte powders and tablets themselves, but it would seem that the following guidelines are a good place to start:

Educate yourself about fluid and electrolyte intake during endurance exercise, and about the symptoms of the various medical conditions that an imbalance can lead to.

If your endurance exercise is going to be taking place in a wilderness environment you owe it to yourself and the other participants to be knowledgeable, responsible and potentially able to recognize symptoms in others who may find themselves in difficulty.

Make sure that the advice you rely on is relevant to what kind of athlete you are.

This is important because research suggests that front runners in a race are more likely to suffer an electrolyte imbalance because they are losing salts and fluid through excessive sweating, whereas middle to back-of-the-pack walkers who exhibit hyponatremia often do so because they are taking on more fluids than their sweat rates dictate they need, and are therefore diluting the sodium levels in their blood stream.

Recognize that individual physiology plays its part, and know your own body.

For example, if you are fit and acclimatized to the climate in which you are exercising you will sweat less than those who are unfit or unacclimatized.

Experiment and practice in your training sessions. Find out how your body feels and reacts to different levels of fluid intake and electrolyte supplements. Find out which supplements you like and which you think you’ll still be able to stomach after five days of intense racing, (many competitors are thankful for salty or un-sweetened products after a few days).

Importantly too, find out how much fluid you lose during the training sessions which most closely resemble your planned endurance activity, by weighing yourself before and after and noting your fluid intake. This will help you work out in general terms how much fluid you are sweating or peeing out compared to how much you are taking in.

Make a plan, buy a sports watch with multiple and repeatable alarms and know how to tweak the plan if necessary.

Many competitors drink a certain amount of fluid and take electrolytes on a planned and consistent basis before, during and after exercise. Generally, these competitors suffer the least number of problems due to hydration and electrolyte imbalance.

If you do have a medical problem out in the field, this information will also be very helpful to the race medics who will be able to more easily identify the cause of your symptoms.

If you don’t have time to get acclimatized before your race, at least try and get one practice run in before the start to help gauge how you might need to tweak your plan.


Useful resources to get started:

Articles based on medical research:

Ian R. Rogers, MD, for the Wilderness Medical Society

Fluid and Electrolyte Balance and Endurance Exercise: What can we learn from recent research?

Hammer: The 10 biggest mistakes endurance athletes makeArticles by electrolyte supplement manufacturers:

Hammer: Electrolyte replenishment and why it’s so important.

Nuun: Hydration 101

Community discussions/forums/blogs:

Ultra Running Resource: Sodium/Salt and Electrolytes

USA Triathlon, Bob Seebohar: Hyponatremia in Endurance Athletes

4 Deserts and RacingThePlanet website:

If you’re new to endurance racing, read blogs from previous RacingThePlanet events to find out how individual competitors fared and what their advice is for others. Find the index here.

Ask our ambassadors like Rob James and Eric LaHaie questions - they have a wealth of experience to draw on and are only to happy to share their knowledge.

Read articles on Hyponatremia, heat illnesses and sunburn in our Expert Advice library.

Click here to see our Hydration And Nutrition Supplements.

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