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Preload Hydration Technique

Updated: Feb 7

Dana Eshelman, MS, RDN, CSSD


When you are exercising, your body begins to sweat in order to control your internal body temperature. This is why you will lose more sweat in hot, humid conditions and less in a cool environment. In either scenario, you are at risk of becoming dehydrated. This is where priming your body with increased fluid volume and electrolytes, or preloading your hydration can make a difference in both your cognitive and athletic performance.


The Importance of Hydration

Losing just 2% of body water weight negatively affects cognitive and athletic performance by increasing fatigue, decreasing reaction times, and decreasing concentration. Most of the water in your body is contained in your vascular system outside your cells. This is called extracellular water. When you are adequately hydrated, your body is able to deliver nutrients and oxygen to your muscles (cardiac output and stroke volume), it allows for better regulation of your core body temperature (heat dissipation) and reduce heart strain (lower heart rate).


When you sweat, water moved from inside our cells into the extracellular space to meet cardiac output. Sweat is comprised of not only water, but also electrolytes including sodium, potassium, magnesium, calcium, and chloride. The amount of fluids and electrolytes lost is highly individual. The nature of endurance training and racing puts you at increased risk for becoming dehydrated as fluid and electrolyte losses exceed intake through the duration of activity. So, you can see where starting your training and racing properly hydrated can make a difference.


What is Preloading Hydration + How to Do It

Preloading your hydration is a technique of consuming a high sodium electrolyte drink (1500 to 3600 mg sodium per liter) in the 15 to 20 minutes before your event has been seen to improve hydration status and improve performance in athletes competing in hot, humid temperatures. However, it is not always the goal to maximize sodium intake (more is not always better). If you are not entering a training session or starting a race dehydrated; or if you are not exerting yourself in hot, humid temperatures, a high sodium solution beverage is not necessary. Something that is closer to 800 mg sodium/ L would adequately hydrate you and provide the same benefits of decreased cardiac output, improved core body temperature regulation and overall aid in performance.


The goal of preloading is optimizing hydration status and boosting blood plasma volume before tough efforts, when you are dehydrated, or for extreme heat, humidity. The extra sodium pulls water into the extracellular space so your cardiovascular system is ready to meet the demands of delivering oxygen to working muscles and cooling you down.


If you find you are a more salty sweater or headed out for an intense session, you may also try preloading with a potassium-rich solution (6-8% daily value). You may also include potassium rich foods in pre-session meal/snack such as, potatoes, banana, dried fruit and yogurt, to name a few.


Preloading is about striking a balance between being able to hold onto fluid without leading to gastrointestinal issues (seen with sodium 4000mg/L) or feeling bloated and sluggish. A solution of 1500 to 3600 mg sodium/L has been well tolerated in athletes and seen to increase plasma volume.


On average an endurance athlete loses over 500 mg of sodium per hour during races, which adds up over the course of training sessions and race days lasting more than 3 hours. I highly recommend preloading to those athletes that are salty sweaters or to those that are going to be out in hot, humid climates.


You can tell if you are a salty sweater if you have a salt residue left on your clothing, hat, or skin after training sessions or races. You may also test your sweat with sweat tests such as NixBiosensor.


Here are some ways to optimize your preloading technique:

  • Include a strong electrolyte drink (1500 mg to 3600mg sodium/L) with 500ml/ 16 ounces of water in the evening before your race. Drink water and decaf beverages as you would on this day. Some great products to include here are skratch hydration or wellness, precision hydration and LMNT.

  • Include a strong electrolyte drink with 500ml/16 ounces of water in the morning or your race day a few hours before race start. Be sure to finish hydration within 45 minutes to 1 hour before the race starts to allow your body to absorb the electrolytes and water.

  • If you suspect you are dehydrated or are doing out for a longer, harder session in the heat, you may try preloading your hydration with a more concentrated solution (nearing 3600 mg sodium/L)

  • Limit your desire to over- consume water or only water as you build up to your race. This can dilute sodium concentration in the blood thereby increasing risk for hyponatremia (aka low sodium in your blood). Ideally, your urine will be a light yellow or the color of lemonade; this will tell you if you are hydrated. You actually do not want your urine to be clear.


Working with a dietitian can help you create a personalized hydration strategy for you. If you are interested in individualized nutrition and support, please apply to our 1:1 coaching.


These links are affiliate links and I do receive a percent of the amount you purchase:



NixBiosensor: Dana15off

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