Overhydration—A Cycling Hidden Danger and a Potential Medical Emergency

Should you take sodium tablets before or during a big event? Exertional Hyponatremia, a danger of overhydration for cyclists, is a life-threatening condition that is avoidable by following these simple steps.

people riding bikes on a beach

Many challenges face a cyclist in preparation and performance. Thoughts of equipment, attire, route, and conditions pervade the thoughts cluttering our minds as we calculate the variables keeping us upright and right where we want to be.

Fueling and hydration are two factors with countless permutations, and it is a significant challenge to get them just right. When cycling, two problems arise when our fluid-electrolyte balance is off—dehydration and overhydration.

A cyclist can enter a dehydrated state when they don’t appropriately replace water and sodium losses in sweat and urine as they ride. When experienced at low levels, this common condition produces little to no performance effects or symptoms. The danger of overhydration for cyclists is a more significant concern that’s often overlooked.

Do you know your Sweat Rate? Follow this link for a deep dive into how to determine how much water you lose riding and what you can do!
image of person sweating after a workout

Moderate to severe dehydration levels adversely affect performance and lead to hydration-related illness in some cases. Many cyclists encounter this condition or know a fellow rider who has. It happens frequently, and most seasoned cyclists know how to prevent and treat the issue—a sensible hydration strategy.

The converse condition occurs when cyclists are unwittingly overzealous in their hydration strategy. The excessive consumption and retention of dilute fluids, although less common, has dire consequences. The danger of overhydration for cyclists is a hidden risk to endurance athletes.

There is little to no evidence that deliberate pre-ride consumption of excess pure water provides a performance benefit. That hasn’t stopped many of us from falling into the trap. It is a hot and humid day, and you want to get in front of your hydration, but you overdo it a bit. Now what?

person reaching for a water bottle during a run

Exertional Hyponatremia is a Potential Medical Emergency-The danger of overhydration for cyclists

Overhydration during exercise dilutes our blood. The imbalance in serum sodium levels causes water to move from our blood into cells. The potentially fatal condition Exertional Hyponatremia (EHN), results as the cells swell.


EHN is one of the few potentially fatal exercise-related illnesses affecting healthy, trained athletes. As an athlete’s blood concentration nears 130-135 mmol Na+/L, they may experience lightheadedness, dizziness, nausea, swelling of the extremities, and baseline body weight increase.


As the concentration dips below 130 mmol Na+/L, the symptoms worsen, and the risk to most athletes increases dramatically. The athlete may suffer headaches, vomiting, frothy sputum, breathing difficulty, and swelling in the lungs. Swelling in and around the brain causes confusion or seizure.

a cruiser bike with basket on a beach

Predisposing Factors of EHN

If you are on the small range as far as cyclists go, have a high sweat rate, and your sweat contains a lot of Na+, you may be at increased risk when engaging in an event of four hours or more. How do you know?


Calculating your sweat rate and comparing it to known values or those of your cycling buddies will indicate. If white salt deposits streak your cycling kit after a long ride, you may secrete excess Na+ in your perspiration. Be careful because you are at increased risk of developing EHN.

cyclist drinking from a water bottle in front of a street sign

Should I Take Sodium Tablets to Avoid EHN?

Supplementation with salt capsules is a widely recognized trend among endurance athletes, and it has been for decades. Old habits die hard, even when science or circumstance doesn’t support the practice. Despite this, a disproportionate number of cyclists take added sodium, believing it eliminates muscle cramps and protects against EHN.


Many life-threatening EHN cases occurred in athletes who had diligently supplemented with salt. The opposite is true of most athletes who don’t take salt during exercise and have no EHN symptoms. Moreover, studies show that sodium supplementation has only a minor effect on increasing blood Na+ levels, if at all.  


However, you should be aware if you notice salt deposits on your cycling clothes after a long and hot day in the saddle. A few days in a row of profuse sweating and excess sodium loss leads to a total-body salt deficiency.


If you have a craving for salt, you may be low, and it’s best to add some savory foods to your post-ride diet. Use dietary recommendations for the amount of sodium in everyday food items and judge accordingly.

salt shaker half filled with salt

A Few Steps You Can Take to Avoid EHN Emergency

1. Measure your body weight before and after exercise:

It is good to know where you stand, even though this method isn’t an ideal water gain or loss reflection.

2. Do not gain weight during endurance exercise:

Fluid retention and a more significant risk of EHN accompany an increase in body weight.

3. Consume fluid at a rate of about 700 ml/h:

The American College of Sports Medicine recommends a 400 to 800 ml/h rate of fluid intake during endurance exercise.

4. Be aware of white salt deposits on your cycling kit:

It may indicate an elevated sweat rate and salt concentration, placing you at higher risk of EHN.

5. Be alert for the symptoms of EHN during exercise performance.
6. Consume your post-ride fluids sensibly:

The symptoms of EHN can develop hours after excess fluid consumption or your event.

7. Develop a hydration strategy:

Use the information you have and the advice of your exercise professional to create a plan—experiment to hone your strategy during training before relying on it in competition.  

biker crashing into a mud puddle


Dehydration is a significant issue for cyclists, but “Waterlogging” your body has potentially fatal ramifications. Be careful to avoid gaining weight during a ride. It may signify that you are retaining fluid and diluting your blood. Be sensible in your hydration strategy and know the signs. It might mean more than just performance—much more!

Your Thoughts?

Have you or anyone you know ever suffered from the adverse effects of overhydration? Comment below! Your fellow cyclists would like to learn from your experience.


For more performance tips and helpful information to ensure that your body is in the best position to succeed, check out the Training & Performance page of The ZOM!

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[…] For a deep dive into the perils of overhydration, check out this The ZOM article detailing the devastating effects of Exertional Hyponatremia.  […]

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