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Is Pre-Hydrating Necessary?


Summer training can be challenging due to having to run in the heat and humidity. To avoid risks of running dehydrated and potentially experiencing dangerous heat related illnesses, such as heat exhaustion, proper hydration is key, but should we be focusing on pre-hydrating?


What is pre-hydration?

This is a fairly new term used in sports nutrition. Throughout my nutrition studies, we were taught to go into a training session well-hydrated, but were never told to pre-hydrate. You may notice the trend of high sodium, lower carb sports nutrition electrolyte drinks, ranging from 500 to over 1800 mg of sodium per serving, claiming to boost plasma levels and sodium stores before you exercise. These products further claim that preloading with high sodium electrolytes can regulate body temperatures, reduce fatigue and muscle cramps so you can perform better at your sport.


Pre-hydrating is usually performed the night before a big endurance event like a marathon, ultra or Ironman, racing longer than 3 hours, and has been supported and recommend by sports nutrition researcher, Dr. Stacy Sims.


The claims of pre-hydrating are convincing. I’ve even tried it before marathons the night before and early morning before race day, but is there enough research to support it?


Can pre-hydrating prevent muscle cramps and prevent dehydration?

Exercise-associated muscle cramps can be painful and derail your sports performance. It was previously believed that dehydration and sodium depletion due to excessive sweating caused muscle cramps; however, recent research does not support this claim and preloading with a high sodium drink before a big event will not prevent this from occurring.


However, pre-hydrating with a high sodium beverage 2 hours before exercise has been shown in small studies to prevent dehydration when exercising in the heat. But does this mean we need to pre-hydrate the day before with electrolytes? Probably not.


Unless you consume a very low sodium diet, less than 1500 mg sodium daily, you most likely get enough sodium from your foods to prevent any electrolyte imbalances. The days leading up to a big endurance event, as long as you are not sweating excessively, all you need to do is drink to thirst and monitor your urine color making sure it’s a pale yellow indicating you are well- hydrated. There is no benefit from drinking excessively before your event than you normally would, placing you at higher risk of diluting your blood sodium levels (hyponatremia) and additional sodium lost in your urine, potentially leaving feeling fatigued and negatively impacting your health.


How should you pre-hydrate?

Your pre-hydrate routine before you start your event should include eating foods with extra salt, like pretzels, soup, or adding salt to your foods. You don’t necessarily need to load up on electrolyte tablets or sports drinks, but the extra sodium will increase the fluid uptake into your bloodstream, increase your thirst sensation causing you to drink a little more, and prevent diluting sodium levels.


The latest hydration recommendations include to drink about 4 hours before your event by slowly drinking 5-7 ml (0.17-0.23 ounces) of fluid per 1 kg of body weight (2.2 pounds). For example, if you weigh 150 pounds, 68.1 kg, you would need about 25-34 ounces of fluid over 4 hours before your event to be well-hydrated. If you only have about 2 hours before your event, it’s suggested to reduce your fluid intake to about 16 ounces (about 2 cups) to avoid any gut issues or excessive urination during the event.


Pre-hydration is not always necessary if you have over 12 hours between workouts or are already well-hydrated before starting your event.


The question remains on whether you need high sodium electrolyte products containing over 1500 mg sodium per serving to adequately pre-hydrate.The research is mixed, but what we do know is that dehydration and consuming excess sodium will not prevent muscle cramps, but starting an endurance event well-hydrated including foods or beverages containing sodium, can be beneficial to reducing body temperatures and potentially preventing

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