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Hydration for Endurance Athletes

We're continuing my Fuel Your Workout blog series by exploring hydration for endurance athletes. Both fluid and salt needs vary greatly among athletes, and thus these two things must be individualized as part of your fueling plan!

This is a huge topic, but I distilled it down to the essentials, including:

This in-depth post will give you all the tips and tools you need as an endurance athlete to stay well-hydrated, no matter the time of year. Okay, let's dive in!

Personalized hydration for endurance athletes

Hydration for Endurance Athletes: Definitions

Let's begin by defining hydration, sweat, sweat rate, and sweat composition, so that you can understand these basic concepts before learning specific hydration strategies.

Hydration refers to any fluid and electrolytes (aka salts) that you consume to replace any losses through sweat, breathing, and peeing.

Sweat is made up of water and electrolytes, and we lose sodium and chloride in the highest concentration. So when you're looking to replace electrolytes in the context of long run losses, focus mainly on sodium chloride (i.e. salt). Sports products often do contain some of the other electrolytes (potassium, magnesium, and calcium), but you can primarily get these in your everyday diet.

Sweat rate is the amount of sweat in ounces that you lose per hour, and ranges from 0.5-2.5+ L/hr. Other factors like temperature, humidity, altitude, and exercise intensity cause sweat rate to fluctuate within one person. You're considered a "heavy sweater" if you lose at least 32 ounces (1 L) of sweat per hour of exercise.

Sweat composition refers to the electrolytes that you lose in your sweat. Like with sweat rate, sweat composition varies from one athlete to the next (200mg-2,000mg+/L), but each athlete's sodium concentration (i.e. mg/L) stays the same in different conditions. You are considered a "salty sweater" if you lose >1,000mg of sodium per liter of fluid.

How to Start All Endurance Sessions Well-Hydrated

First, make sure that you are meeting your baseline hydration needs, which you can calculate by taking your weight in pounds and dividing by 2. This gives you your daily fluid goal in ounces, and does not include additional needs due to exercise. Aim to drink consistently throughout the day, and meet these needs via water, seltzer, juice, tea, coffee, milk, or whatever other beverages you enjoy (except alcohol).

Then, focus on hydration before exercise. I covered this topic in my last two blog posts (before a shorter session and a longer session), but here's a recap:

  • If you have 2+ hours before training, drink ~16-24oz of fluid with your meal or snack.

  • If you <1 hour, drink at least 8oz of fluids.

  • If you're a very heavy sweater (>1.5L/hr), add another 8oz 30min before you go.

Again, fluids can come from water, tea, coffee, juice, sports drink, milk etc. Keep in mind that you absorb water better when you consume it with electrolytes and carbs. So include a sports drink if it's hot out, you're a heavy and/or salty sweater, or if you're about to start a key training session or race.

Preloading / Hyperhydration

Preloading or hyperhydrating helps you begin exercise well-hydrated. This strategy involves consuming extra fluid and sodium above your baseline amounts the night before and/or morning of a long or hard effort. Doing this boosts your blood plasma volume (i.e. improves hydration status), which enhances your performance. It's particularly useful if you are a salty and/or heavy sweater and if it's warm out.

The question is, how much extra sodium should you consume? Too little, and you don't accomplish the goal. Too much, and you cause GI distress. The sweet spot seems to be roughly 1500mg in about 32oz of water (or 750mg in 16oz), but we can give a range of 1500 to 2000mg sodium per 32oz fluid, with whatever carbs you're consuming.

How to preload or hyperhydrate with salt and water to begin exercise well hydrated

As you can see, you can hyperhydrate with food, high sodium drinks, or a combo of both.

For instance, include extra salty foods in your dinner the night before a long training session or race, like soy sauce, pickles, pretzels, salted pasta with tomato sauce or chicken broth, and drink 16-32oz of plain water on top of your daily fluid needs. Or, use a sports drink (e.g. Precision 1500 has 750mg per packet, and you mix with 16oz of water to get 1500mg/L).

There is never one "right" way to fuel or hydrate. There are lots of options and you can experiment to figure out what works best.

Fluid Goals During Exercise

Fluid goals during exercise depend on many factors, including your exercise duration, sweat rate, and environmental conditions.

You may not need to carry fluid during a short session (<60 min) if you begin hydrated and rehydrate after. But if it's a warm day, and especially if you're not adequately hydrated before and/or you're a heavy sweater, carry water or sports drink and sip to thirst.

You need to carry fluids during all longer sessions (>60 min) if you care about your health and performance. A generic range for fluid intake during endurance exercise is 12-28 ounces per hour, or higher for heavy sweaters. Keep in mind that you should NOT be trying to replace your fluid losses 100% during exercise. Instead, the goal is to replace 50-75% or slightly more, depending on how much you lose.

How to estimate your fluid goal per hour

The first step to estimating your fluid goal per hour is to determine how much fluid you are losing. You can do this by reading my blog post with step-by-step instructions on how to measure sweat rate. This is an easy, free test that you can do at home with a scale to individualize your fluid goals. Ideally, you do this test more than once, in different conditions.

Then, use your sweat rate to personalize your fluid goals:

  1. If your sweat rate is >32oz/hr, aim to drink at least 24-28oz/hr during your run.

  2. If your sweat rate is >1.5-2L/hr, then you need to consume closer to 1L/hr or higher. Just note that this is something you have to practice in training. It can be hard logistically and physically to take in more than 1L/hr over long periods of time.

  3. If your sweat rate is <1L per hour, aim to replace 50-75% of losses. For instance, if your sweat rate is 24oz/hr, aim for 12-18oz/hr.

Here are some things to keep in mind about fluid goals:

  • Figure out how much you currently drink per hour during longer sessions. That way, you can compare your baseline intake to your goal intake, and gradually work up to it if there's a big difference.

  • Drink on a schedule to hit your fluid goals. Thirst is important, but not always reliable, and it's usually a late sign that you need fluids. If you find it hard to drink, try flavored fluids like sports drinks, which help stimulate thirst.

  • Adjust for the weather as well as the intensity of your workout. If you measured your sweat rate on a cool easy run, and you're doing a hard effort in the heat, you'll be losing more fluids and thus need to take in more.

  • Consider logistics - how much fluid you need to carry, what gear you have to carry it, and what (if any) opportunties there will be to refill. You may be fine with a small handheld or belt, or you may need a hydration vest. It's good to have options, especially if you're training in different conditions, so get some gear you like.

Sodium Goals During Exercise

Sodium goals during exercise also depend on several factors, including sweat rate and sweat composition.

If you're interested in testing your sweat composition, you have several options. My favorite is Precision Hydration - this is a test you do at rest, and there are various testing centers around the country. If you don't live near a testing center, Levelen has a kit that you can use during exercise and send in by mail. There are also wearable devices you can use.

Testing isn't necessary for everyone, but if you find that you struggle in the heat, you suspect you may be a very low or high salt sweater, and especially if you're doing ultraendurance events, it's a great way to take the guesswork out of the equation.

How to estimate your sodium goals

If you test your sweat composition, you can use that information to guide your decision on which sports drink (or other things) to use to achieve that concentration. For instance, if you lose 1000mg/L, you could pick a product like LMNT or PH1000 (both give 1000mg/L) and drink as much as you need to reach your fluid goals. Alternatively, you can use a combo of foods, gels, salt pills, and drinks to reach your goal.

If you don't test your sweat composition, look for signs that you are a salty sweater like white stains on clothing, salt on skin, struggling during long training sessions or races especially in the heat, having salty tasting sweat, or having sweat that stings your eyes. You can also pay attention to cravings for salty foods or fluids. If you don't experience any of these things, then you may be fine with a more moderate intake of salt.

If you're not sure where to start, a generic recommendation is to consume 500-800mg of sodium per L, and see how that feels.This is around or just below the concentration of many common sports drinks. If you think you are a salty sweater, you may want to start at the higher end of this general range if not slightly higher.

For reference, if mixed as directed, Gatorade Endurance Formula has a concentration of ~820mg/L, while Tailwind Endurance Fuel has ~840-1,000mg/L. Other products depend on how many scoops or packets you use, and in how much water. Again, there's no one right way to do this. We will go over some example products and foods shortly.

Here are some things to keep in mind about sodium goals:

  • Sodium is a concentration-based goal (mg/L), while carbs and fluids are time-based goals (grams or ounces per hour). It's fine to talk about sodium as mg/hr, but this must be tied to your fluid intake. You can calculate your hourly sodium target once you know how much fluid you need.

    • E.g. If your sweat contains 1000mg/L of sodium, and your fluid goal is 16oz/hr, then you need 500mg of sodium/hour, and you can get salt from sports drinks, food, gels, salt pills etc.

  • You are not replacing 100% of your sodium losses, just as you are not replacing 100% of your fliud losses. But the sodium concentration of what you're consuming needs to be close to the sodium concentration of your sweat.

    • E.g. Using the example above, let's say your sweat rate is 24oz/hr. You're losing >650mg of sodium, but since you're only drinking 16oz, 500mg is adequate to achieve a concentration of 1000mg/L.

Hydration After Exercise

Hydration after exercise depends on your sweat rate, as well as how well of a job you did drinking during your workout!

The key thing to note is that you need to drink more fluid than what you lost via sweat - the exact number is 125-150% of your losses (go back to your sweat test results). So for every 1 lb you lose in sweat, you need 20-24oz to replace it. Aim to consume this total amount of fluid within 4 hours of finishing your workout.

Haven't done a sweat test yet? After you finish exercise, drink at least 16-24oz of fluid. This can be water plus a salty carb-rich snack/meal or a carb-containing sports drink.

There are many ways to get fluids in - water, sports drinks, and juice, water-rich fruits like watermelon, smoothies, protein shakes, etc. Pay attention to what you're craving and what tastes good, and eat more salt if you crave it.

How to Choose Your Sports Nutrition Products

There are a ton of sports nutrition products on the market, and they are all different in terms of taste, texture, flavor and nutrition profile. Choosing which ones to use can be overwhelming, but don't worry - I'm here to help with that!

When choosing your sports nutrition products, consider:

  • What kind of gear is comfortable and allows you to adequately hydrate and fuel, both in training and in competition?

  • Do you have low, moderate or high fluid and/or sodium needs? This will guide your product decisions.

  • What type of event are you doing, and do you like the products that are offered on course?

    • In a road marathon, you may prefer not to carry anything except gels and drink the sports drink at aid stations, or choose higher sodium gels and drink water. In a long-course triathlon or ultramarathon, you may prefer to bring your own sports drink and fueling options, but also eat at aid stations.

  • What are your individual preferences or tolerances? Do you like the taste of sports drinks or do you prefer plain tasting products or water?

  • Are you training in different environments? For instance, if you're training in the cold for a warmer spring or summer race, or training in the heat for a cooler fall race, you likely need a variety of products to use in training and racing.

All of this will help guide the process of choosing products, not just for your fluid and sodium needs, but for all fueling goals.

Popular sports products and foods with varying levels of sodium

Here are some visuals of common sports drinks, salt pills, gels, chews, and foods that I've categorized for you. This is not an exhaustive list, but a sampling of what's on the market. My goal is to show you the wide range of sodium that is provided in these different products (they also have vastly different carb contents too).

FYI, these numbers represent the amount of sodium per serving of the pictured product (e.g. 1 scoop of Tailwind or Skratch). And remember, how you mix products (i.e. how much fluid you use) changes concentration!

Low, moderate and high sodium fluids

Salt pills typically have ~200-250mg/capsule, depending on which brand you pick. They're handy if you prefer unflavored tastes and just want water and salt, or if you have really high needs and need to add on to whatever else you're doing. They can also give some flexibility, for instance, if you need a break from flavored sports drink and need salt from somewhere else. Always take each pill with water, and adjust fluids to reach he concentration you're trying to achieve (e.g. 8oz water per 250mg pill to give 1000mg/L).

Lower sodium fluids can be useful for low salt sweaters, or if you're getting salt elsewhere (like food, gels etc). Maurten, for example, has 160-200mg per serving, and directions say to mix with 16oz, giving roughly 320-400mg/L.

Moderate sodium fluids are your most common products, as they capture that generic recommendation that I mentioned earlier of roughly 500-800mg/L, with some slightly higher depending on how you mix it. For example, PH500 gives 500mg/L (1 packet has 250mg, and you mix in 16oz), while 2 scoops of Tailwind in 20-24oz gives 840-1000mg/L. Skratch sport and everyday hydration mix both have 400mg per scoop, which you can mix as desired.

Lastly, high sodium fluids will give you 1,000mg/L or higher. Liquid IV has 500mg (mix in 16oz to give 1000mg/L), PH1500 has 750mg (mix in 16oz to give 1500mg/L), and LMNT has 1,000mg (mix in 1L), while Skratch very high sodium and the Right Stuff have over 1700mg per serving. Use these products if you're a salty sweater or to hyperhydrate.

Low and high sodium gels and chews

Now let's chat about gels and chews. I tried to include most of the popular products I see in my practice and out on race courses. Keep in mind that different flavors of the same product will sometimes vary in sodium content.

Many gels and chews contain very little sodium. Sometimes, like with Precision's line, this is intentional. They want to keep carbs and salts separate. Other times, it's not so clear why the sodium amount is what it is.

In the zero to minimal sodium category are Maurten, SIS, untapped, Hammer, Precision gels and chews, Skratch chews (1 serving), and honey stinger chews.

In the lower sodium category, we have Ucan edge (55mg), and then Huma, SIS with electrolytes, Muir and the 2x sodium Clif Bloks (all around 100mg).

Lastly, in the higher sodium category, we have GU regular and roctane (125mg), and Never Second, Huma+, Powergel and Clif blocks 3 x sodium (over 200mg).

So you have many options, and can choose whichever product or combo of products meets your needs and preferences. I encourage you to go to a site like the The Feed or visit your local sporting shop to try a variety of drinks, gels and/or chews, and see what works for you.

Foods for ultrarunners that provide sodium

Solid foods can also provide sodium, as well as a welcome change of flavor, texture, and some other needed nutrients. This becomes particularly important in ultra endurance events, like ultramarathons, cycling, and long-course triathlons, for example. Your specific sport and event, as well as your tolerance, will dictate what's available and what you eat.

I've listed above some popular high sodium foods that you may see people train and race with as endurance athletes. Pretzels are great - I personally like the flat ones with extra salt - though they're very dry so they don't work for everyone. Potato chips are a classic aid station food, and the fat makes it more palatable. Some people like PB&Js, while others enjoy salted mashed or boiled potatoes.

Quesadillas are great for longer races where you need something more substantial. Broth or noodle soups are a great choice in colder events, while salted watermelon is a great summer option. Some bars have a decent amount of sodium too (e.g. Maurten's has over 200mg sodium and Clif is around 150mg).

Hydration in Different Conditions

Let's wrap up this post with how your hydration needs change in different environmental conditions, and how you can adjust your plan accordingly. It's nearly summer, so warm weather is on most of our minds, but you need to pay attention to hydration year-round!

Heat increases our sweat rate, which leads to more fluid and salt being lost. That means we need to increase the amount of fluid per hour with adequate sodium to make up for these increased losses. Remember - if you lose MORE sweat per hour, you lose more total sodium because the total volume of sweat is higher, but the mg/L doesn't change. Heat can also mess with your ability to fuel - it's crucial that you stay on top of your hydration so that you don't add GI issues to the mix.

Hot and dry is really different than hot and humid. Increased humidity can lead to increased perceived effort. That's because your body produces heat that it needs to get rid of through sweat. In a dry environment, the sweat can evaporate easily and dissipate heat but in a humid one, the air is already saturated with water and sweat pools on the skin and drips off, taking much less heat with it from the body. This is where looking at a heat index can be helpful, to get a better sense of what the air feels like versus the actual temperature.

What about cold? I often see people neglecting their hydration in cooler weather and especially in below freezing temps. But there are multiple physiological things going on that cause you to still get dehydrated.

You have a decreased thirst sensation, making you less likely to drink unless you're intentional and drinking on a schedule. Also, you may need to pee more frequently in the cold, due to cold induced diuresis. Blood flow is flowing away from the skin and towards the center of the body to protect your organs from the cold, which forces the kidneys to filter more blood and thus produce more urine. As a result, you have an increased urge to pee and you lose more water.

You're also still sweating, even though you may not notice it as much because the air is dry and tricking you into thinking you're sweating less. And lastly, you need to practice cold weather specific fueling strategies to prevent fluids and other fuel from freezing.

Here are a few cold weather fueling tips:

  1. If you're using a hydration bladder, blow back into the tube after drinking so it doesn’t freeze, and wear your pack under a jacket to keep body heat in. You can also use an insulated tube. If you're using bottles, wrap wool socks around them.

  2. Use a little splash of vodka to lower freezing temp in your sports drink.

  3. Use higher carb drinks to lower freezing point and get more calories from liquids

Lastly, high altitude, which is anything over 8,000ft, increases risk of dehydration. With less oxygen, your breathing becomes faster and shallower, contributing to increased water loss. And similar to the cold, the air may be less humid, causing moisture to evaporate more quickly, making you think that you're sweating less than you are.

Also, like with cold, there is high altitude diuresis, where your kidneys react to drier climates and regulates the thickness of your blood to carry oxygen, causing increased urine production and thus fluid loss. Like with heat, GI issues are often more prevalent at altitude. One strategy that works well is taking smaller but more frequent sips of fluids to stay hydrated while not overwhelming the gut.

Want to learn more? I have some additional resources for you!

My podcast episode with Sports RD Colette Vartanian from Sktrach Labs is a great deep dive into personalized hydration strategies and testing methods, and this episode with Andy Blow from Precision Fuel & Hydration is another fantastic overview of personalized hydration concepts and testing. Both are geared towards endurance athletes and will give you a solid background on all things hydration.

My Hydration Mini Guide & Sweat Test Worksheet is a resource that includes much of what I'm discussing today, in digital download form. My FREE Winter Fueling Guide specifically focuses on hydration and fueling in cooler temps.

Lastly, if you found this post helpful, you will love my self-paced course Peak Performance for Endurance Athletes: Your Ultimate Guide to Strategic Fueling. This 7-part series is packed with evidence based, easy to understand information with tons of visuals covering everyday nutrition, hydration, intraworkout fueling, training the gut, performance and micronutrient supplementation, and preparing for race day. Preview the course, the full curriculum, and get all your questions answered here.

Questions? Comment below or get in touch.


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