How to hydrate for endurance sports

Endurance sports place heavy demands on our bodies. When you exercise for hours, your fueling, recovery, and hydration (including electrolytes) need to be dialed in — not just to make it through a training session or event, but to feel well doing it.

But you don't need to calculate and replace your precise water and salt losses to feel and perform your best. It can be helpful to learn how much water to carry, or how many aid stations to hit along the course, but it's time and labor-intensive to calculate. I'm a hydration nerd, but I'm also big on simple guidelines that are easy to follow. 

A general rule of thumb to hydrate for endurance sports? Include 1 gram of sodium in 16–32 ounces of water, and then drink that electrolyte water to thirst before, during, and after your activity.

Following this science-backed guideline helps keep your fluid intake at a Goldilocks level — not too little, not too much — while replacing sweat sodium losses. You may just perform and recover better, too.

Drinking electrolyte water to thirst is the big takeaway today, but there's lots more science on endurance hydration if you have the stamina for it (pun definitely intended). Let's start with what happens when folks get too little or too much fluid during exercise. 

Does Dehydration Impair Endurance?

A fair bit of research suggests dehydration (net water loss from the body) does impair endurance performance: 

• A 2010 meta-analysis of 29 studies concluded that losing 3% or more of one's body weight in water decreases power output during endurance exercise.
• A 2015 study found that dehydrated cyclists (2–3% body weight loss) had higher heart rates, rates of perceived exertion, and core body temperatures, and performed 13% more slowly on time trials. 

Dehydration is common during endurance sports because athletes can lose considerable fluids through sweat — up to 10 liters/day in warm climates, according to a paper from the Journal of Sports Sciences. 

This paper sheds light on why dehydrated athletes may not perform as well. According to the authors, their hearts may work harder, and their cooling mechanisms may be impaired.

This makes sense. Being dehydrated means blood volume decreases. Consequently, the heart must beat faster to deliver the same amount of blood (which is carrying oxygen and other nutrients) to the body, including muscles. The heart working harder means fatigue sets in more quickly. Plus, dehydration can decrease sweat rate, impairing the body’s ability to cool itself and potentially decreasing performance. 

But while this science suggests dehydration can hinder endurance performance, drinking too much water can be a problem, too. 

Overhydration in Endurance Sports

Drinking plain water beyond thirst can lead to the opposite of dehydration: overhydration. Excess fluids dilute blood sodium levels, which can lead to fatigue, headaches, brain fog, muscle cramps, or more serious neurological symptoms requiring medical attention. 

Overhydration is unfortunately common in endurance sports. These athletes often drink water on a set schedule in an effort to prevent dehydration, a practice encouraged by institutions like the American College of Sports Medicine.

We break down exercise-associated overhydration in depth here. But the bottom line is that including electrolytes in your rehydration strategy can help prevent overhydration. Let’s talk about those electrolytes now.

Sodium for Endurance Hydration

Sodium is the primary electrolyte lost in sweat, with some athletes losing up to 7 grams daily when exercising vigorously in warm climates. Replacing those sweat sodium losses not only helps prevent overhydration from drinking plain water, but may support endurance performance for two more reasons: 

1. Sodium supports fluid balance, which supports blood flow, sweating, brain function, and more.
2. Sodium supports the sodium-potassium pump, a part of every human cell that helps nerve impulses to fire. The sodium-potassium pump allows cells to “talk” to each other, contract muscles, and more.

I’ve seen many athletes skip sodium in their hydration strategy. I skipped it myself for years! Many folks may be surprised at how replacing both fluid and sodium losses can have an outsized impact on how they feel and perform.

How Much Water and Sodium Do You Need for Endurance Sports?

The amount of fluids and electrolytes you’ll need to replace sweat losses depend on sweat rate and sweat sodium concentration. You can calculate both, or use our Sodium Intake Calculator for an estimate for the salty part of the equation, but the simple rule of thumb I shared in the beginning will do the trick in most cases: Drink electrolyte water to thirst before, during, and after exercise. Here’s why this guideline can work.

Drink to thirst

Thirst is your built-in system for guiding fluid needs. When your body needs more fluids, thirst ramps up. As you drink water and “fill the tank,” thirst shuts down. That’s why drinking to thirst (and not beyond), helps prevent dehydration and overhydration.

Listening to thirst works in most cases, but age and cold weather or high elevation can affect the thirst mechanism, often requiring a shift in hydration strategy. But in most cases, thirst is a great (and simple!) guide to hydration needs.

Add electrolytes to your water

Studies suggest athletes can lose approximately 0.5–2 grams of sodium per liter of sweat, with an average of about 1 gram/liter. Including ~1 gram of sodium per 32 ounces (~1 liter) of fluid can help replace these losses, though “salty sweaters” may do better with 1 gram per 16 ounces of fluid. Play with your sodium-to-liquid ratio while drinking to thirst — you'll feel the difference when you get it right.

Factors increasing fluid and electrolyte needs

As you’ll recall, sweat rate and sweat sodium concentration influence hydration needs during endurance sports. Both of these are affected by a variety of inputs.

Factors that increase sweat rate include greater ambient temperatures, humidity, exercise intensity, aerobic fitness, body weight, heavy clothing, and heat acclimation. Factors that decrease sweat rate include airflow (as in, oh yeah, that breeze feels nice) and dehydration.

What about sweat sodium concentration? Anything that increases sweat rate (like intense exercise) can make sweat saltier, increasing sodium losses. There's also lots of individual variability. The saltiest sweaters can have 4–5 times more sodium in their sweat than the least salty.

Planning for Endurance Hydration

For many folks, including 1 gram of sodium in 16–32 ounces of water and ensuring you have access to your water bottle while you work out — or have the ability to refill it — will do the trick. Your body will guide your hydration needs.

For those who are going longer distances and carrying all their water with them, planning how many bottles to stage along a course, or want an extra edge, you may want to determine your exact sweat losses by calculating your sweat rate and sweat sodium concentration.

Precise calculations can help with planning, but you may still want to rely on your thirst signals to determine when and how much electrolyte water to consume. Sweat losses can vary considerably by activity and environment, and drinking to thirst rather than on a set schedule can allow your body to adjust your hydration strategy to the situation.

We designed LMNT with 1 gram of sodium in each stick pack and can to provide an easy option to hit that 1 gram per 16–32 ounces of water target. DIY fans can also try our electrolyte homebrew recipes, or simply shake ½ teaspoon of salt (~1 gram sodium) into a liter of fluid. It'll taste like mildly salty water, but some folks don't mind that.

However precise you get with your calculations and whichever rehydration strategy you choose, Stay Salty in your training and on the race course, and don’t forget to have fun!