When we talk about long races, two fears often come to mind:
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"Am I going to get a cramp?"
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"Could I get sick from drinking too much water?"
Behind these doubts lie two different things:
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Fluid and electrolyte balance (water and mineral salts, mainly sodium);
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A more serious condition called exercise-associated hyponatremia occurs when the concentration of sodium in the blood drops too low during or shortly after prolonged exertion. ( PMC )
This text is a guide to help you understand:
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How sweat, sodium, and hydration work;
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What science says about cramps and hyponatremia;
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Practical ranges of fluid and sodium intake per hour ;
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and a step-by-step guide to building your own strategy.
Important: This content is for educational purposes only and does not replace consultation with a doctor or nutritionist, especially for those with a history of high blood pressure, kidney problems, or heart problems.
1. What happens to the body when you sweat?
During exercise, especially in the heat, the body uses sweat as a cooling system. This sweat contains:
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water
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and electrolytes, mainly sodium (Na⁺).
Studies with athletes show that: ( PMC )
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The sweat rate typically ranges from approximately 0.5 to 2.0 L/h.
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The concentration of sodium in sweat varies on average from ~10 to 90 mmol/L (approximately ~230 to ~2,070 mg of sodium per liter).
I.e:
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Some people lose very little sweat and very little sodium .
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Others lose a lot of sweat and a lot of sodium (the classic "crystallized salt" on clothes, white cap after training, etc.).
This explains why there isn't a single perfect number of milliliters or milligrams for everyone.
2. What is exercise-associated hyponatremia?
Hyponatremia occurs when the concentration of sodium in the blood falls below 135 mmol/L.
When this happens during or up to 24 hours after prolonged exercise, we call it exercise-associated hyponatremia (EAH) . ( PMC )
The international consensus led by Tamara Hew-Butler and Mitchell Rosner highlights two important points: ( Emergency Medicine Cases )
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Most cases occur in long-distance races (marathons, ultras, Ironman).
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The main risk factor is usually consuming excessive fluids , especially highly diluted drinks or plain water, causing body weight to increase during the race.
Symptoms can range from:
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mild (headache, nausea, dizziness)
until -
severe (mental confusion, seizure, coma).
Therefore, the most modern guidelines have a clear message:
Avoid both severe dehydration and excessive fluid intake .
3. And what about cramps? Are they just a lack of salt?
Here enters one of the greatest myths of the sport.
Recent studies and reviews on exercise-associated muscle cramps (EAMC) indicate that:
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There is no strong evidence that sodium, in isolation, is the primary cause of cramps. ( PMC )
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Muscle cramps seem to have multiple causes : neuromuscular fatigue, exertion beyond what is usual, individual history, heat, electrolyte imbalance – all mixed together.
In studies with ultramarathon runners, for example, sodium supplementation did not consistently reduce the occurrence of cramps, dehydration, or hyponatremia when compared to those who did not supplement. ( SpringerOpen )
This doesn't mean sodium doesn't matter; it means that:
Just taking salt capsules doesn't "guarantee" that you won't get cramps.
Proper training, intensity control, heat acclimatization, and good hydration are also important factors.
4. How much liquid per hour makes sense?
The American College of Sports Medicine (ACSM) suggests that fluid replacement should aim to: ( PubMed )
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minimize body weight loss through sweat (ideally <2% of weight);
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Avoid weight gain (a sign that you are drinking too much);
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Maintain comfort and performance.
The consensus on hyponatremia and other more recent studies reinforce the idea of "drinking according to thirst" as a safe strategy for most athletes, especially in long-distance events. ( Emergency Medicine Cases )
In practice, many endurance athletes end up in a range of approximately:
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0.4 to 0.8 L/h (400–800 ml/h),
Adjusting to:
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temperature;
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intensity;
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body size;
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personal history (some tolerate it more, others less).
How to estimate your sweat rate
A simple method, used in studies and in practice, is:
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Weigh yourself without clothes before a long workout.
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Record how much you drank and if you went to the bathroom.
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Weigh yourself again after your workout (also without clothes).
From this, it's possible to get an idea of how much fluid was lost per hour. Guides like those by researcher Lindsay Baker explain similar methods for estimating sweat rate and sodium loss. ( PMC )
This estimate doesn't need to be perfect; it serves as a basis so you don't drink "in the dark."
5. How much sodium per hour?
As we have seen, the concentration of sodium in sweat varies considerably:
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In many athletes, it ranges between 20 and 80 mmol/L , which is approximately equivalent to 460–1,840 mg of sodium per liter of sweat . ( PMC )
If your sweat rate is, for example, 1 L/h, your sodium loss could be something like:
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~500 mg/h (less "salty" profile),
until -
~1,500–1,800 mg/h (very “salty” profile).
Since not everyone has access to sweat testing, many professionals use practical strips to establish a starting point, such as:
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Something around 300–600 mg of sodium per hour for many athletes;
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which can increase to 600–800+ mg/h in cases of:
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very hot and long races;
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Athletes who report extremely salty sweat;
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History of decreased performance, dizziness, or feeling unwell in very hot situations.
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A recent review on sodium intake in athletes reinforces that:
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Sodium strategies should take into account total sodium from beverages, food, and supplements ;
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The relationship between sodium and cramps/hyponatremia is more complex than common sense suggests. ( PMC )
6. Step-by-step guide to building your fluid + sodium strategy
Step 1 – Understand your context
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Type of race (estimated time, elevation gain).
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Expected weather (cold, mild, intensely hot).
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Personal history:
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Do you usually lose a lot of weight during races?
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Have you experienced symptoms such as dizziness, swelling, headache, or nausea?
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Have you ever been diagnosed with hyponatremia?
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Step 2 – Estimate your sweat rate
Use the before/after weighing method in 1–2 long, race-like training sessions:
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Did you lose 1 kg in 1 hour? That's approximately 1 L/h of sweat.
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Did you lose 0.5 kg in 1 hour? Approximately 0.5 L/h.
Remember that variations of a few percent are normal; it's not an exact science.
Step 3 – Define a fluid intake range
Based on your data and your level of thirst:
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If you lose approximately 1 L/h, it might make sense to drink something like 0.6–0.8 L/h;
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if you lose ~0.6 L/h, something like 0.4–0.6 L/h may be sufficient.
Always watching:
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avoid gaining weight during the race;
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not feeling the discomfort of "being too full".
Step 4 – Plan the sodium
Start with a practice strip, for example:
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300–500 mg of sodium per hour in moderate-intensity tests;
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going up:
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if the test is very hot and long;
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You are clearly a "salty sweat".
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Add up everything that comes in:
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sports drink;
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electrolyte capsules;
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gels containing sodium;
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Salty foods (broth, chips in freezers, etc.).
Step 5 – Testing and adjustment
Use long training sessions to:
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Try different combinations (more sports drink, less capsule, etc.);
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Look for signs such as:
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Very thirsty or dry mouth (may be drinking too little);
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A feeling of "too full" stomach or bloating (perhaps due to too much fluid);
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Headache, nausea, confusion, persistent cramps → always deserve close attention and, if intense or prolonged, medical evaluation.
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7. Warning signs: when the yellow (or red) light comes on
Some signs that may indicate something is wrong with hydration/electrolytes:
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A sudden drop in performance disproportionate to the effort;
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Dizziness, blurred vision, confusion;
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severe headache;
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persistent nausea or vomiting;
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Swelling in the hands, feet, or face;
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recurring and debilitating cramps.
These symptoms are nonspecific – they may be linked to dehydration, hyponatremia, heat exhaustion, or other causes.
Therefore, in more serious or persistent situations, the recommendation is always to stop, ask for help, and seek professional evaluation .
8. How does Z2 fit into this equation: Power Powder and Saltz
Understanding fluids and sodium is the first step. The second is having products that make it easier to put this strategy into practice in daily training and competition.
At Z2, two products fit directly into this theme:
Power Powder – carbs + electrolytes in the same bottle
Power Powder is your hydration and energy "combo":
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It provides carbohydrates to maintain pace during longer training sessions and races.
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It delivers sodium and other electrolytes directly into the drink, helping to replenish some of what is lost through sweat.
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Allows for easy adjustment:
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How many grams of carbs do you consume per hour (serving/scoops per bottle)?
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How many ml per hour do you drink, according to your sweat rate?
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It works very well as the basis of a hydration plan , especially in:
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long running and cycling workouts;
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brick blocks (bike + race);
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tests where you prefer to drink a good portion of what you need for energy and sodium.
Saltz – a sodium boost when the heat intensifies.
Saltz, on the other hand, acts as a tool for fine-tuning sodium levels.
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Each capsule contains a defined amount of sodium and electrolytes , which makes it easy to calculate mg/h.
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It is especially useful for:
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Athletes who sweat a lot and leave their clothes "splattered" with white;
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Very hot and long races, where the sodium from the drink alone may not be enough;
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situations where you need more sodium without significantly increasing your fluid intake .
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In practice, many athletes use:
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Power Powder as a base (carbohydrate + liquid + a portion of the sodium);
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Saltz as a supplement, adjusting the dose according to the duration, heat, and the body's own response.
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