Updated: Jul 9, 2022
Dana Eshelman, MS, RDN
Preloading is a technique in which you drink a strong electrolyte drink usually consisting of 1000 mg sodium or higher the evening before and the morning of race day. This allows your hydration status to be optimal as well as boosts blood plasma volume before tough efforts. The extra sodium pulls water into the bloodstream and keeps it there so your cardiovascular system is ready to meet the demands of delivering oxygen to working muscles and cooling you down.
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 Levelen and Gatorade.
Here are some ways to optimize your preloading technique:
Include a strong electrolyte drink (>1000 mg sodium) 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 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.
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. Ideally, your urine will be a light yellow or the color of lemonade; this will tell you if you are hydrated.