What Science Tells Us About Exercise Hydration


Mike Molloy, Ph.D.  |  Founder: M2 Performance Nutrition

Editor's Note: Dr. Molloy (pictured above) received his Ph.D. from Dartmouth Medical School. His R&D background and status as an elite athlete puts him in a unique position to come up with scientifically-backed nutritional strategies, as well as to experiment with emerging techniques that show promise.  Dr. Molloy's results speak for themselves... 10 of his elite clients competed in the most recent Reebok CrossFit Games.

Is Hydration As Simple As "Filling Up Big Bags Of Water?"

Everyone's probably heard the statement that we humans are just big bags of water, and that's fairly true with 50-60% of our total body mass being water. FYI, men are a little higher on that average and women are typically a little lower. No surprise, but water is extremely critical for pretty much all of the functions that occur in the body at a cellular and organ based level. Water in your body basically is divided into two major compartments; the intracellular fluid (inside the cell membrane) and extracellular fluid (outside of the cells), your blood fluid being a perfect example. While both ICF and ECF are still water, they're actually pretty different as it relates to electrolytes with ICF being higher in potassium and magnesium and ECF being higher in sodium and chloride.

What Are The Different Ways That We Get Water Into And Out Of Our Body?

IN: No shocker here, drinking water and water based products. However, most foods contain a solid water component as well, notably fruits, veggies and water cooked carbs like rice and oatmeal.

OUT: Breathing, evaporation from the skin, sweating, urination and feces (AKA going Number 1 and Number 2).

Should I Just Drink When I'm Thirsty?

One of the major questions that we get is whether you can trust your thirst level to judge when to drink more fluids. As is common in the nutrition world, the answer is "it depends." Most of the time, your body doesn't generate a "thirst" response until about 1.5% of water is lost. Now if you're inactive, thats not a huge deal, but from an athletic performance point of view, its huge. Add on top of that the individual response to exercise ("sweater" vs. "non sweater") and making generalized statements about this topic is extremely difficult.

What science-based recommendations can we make? The Institute for Medicine determined that an adequate intake for men is ~3 liters and ~2.2 liters for women. Of course, there's a bunch variables that could cause you to want to drink more (and sometimes less) than these amounts. Another approach is to use your urine color as an indicator of hydration. Aiming for a goal of "slightly yellow" with ~5-6 urinations through a day seems to be a helpful goal for most people. Of course, supplements that have yellow coloring such a multivitamins, B vitamins, tumeric, etc. can skew the urine color so just just aware of that when considering this approach.

As a performance based nutrition coach, I'm definitely interested in how dehydration can impact human performance. We do know that the 1-2% dehydrated state can have a fairly large impact on performance in both endurance and more strength based efforts. However, we also know that OVER-hydrating can have negative impacts on performance as well if hyponatremia (low blood sodium levels) occurs. In extreme cases, this can actually be life-threatening.

What Should I Drink During Exercise? 

Athletes should be drinking about 8-10 ounces of water 20-30 minutes prior to exercise with another 5-7 ounces for every 20-30 minutes of exercise that follows, in an ideal world. For longer efforts, adding some carbohydrates to the water can improve the absorption of water into the blood circulation, along with any electrolytes that are included as well. Interestingly, several amino acids are also capable of helping to improve hydration as well, notably glutamine, alanine cysteine and glycine. All that said, most research indicates that exercise sessions lasting an hour or less are not negatively impacted by simply drinking water.

Should I Be Mixing Supplements Into My Water?

There's only a few things that I think are worth giving a try. Remember, everyone's a little different so ultimately your response to these approaches will be different as well.

  1. Himalayan salt: There is some evidence to show that a small dose (a pinch?) of Himalayan salt can help remove some of the burden we place on the adrenal glands through our day to day stresses. I personally keep the dose small and just do it for a single glass of water in the morning.
  2. Magnesium citrate: You might be surprised to learn that ~75% of Americans are deficient for magnesium. This is important because studies show that low magnesium levels can impact testosterone production, increase blood pressure and also reduces the efficiency of neuromuscular firing. Dosing can range from 300-500 mgs for the average person.

Is There Any Benefit To "Alkalized" Or Alkaline Water?

There's a hypothesis that an acidic diet (from both food and water) will impact blood pH and cause disease. It's important to note that blood pH is an extremely tightly regulated process and ordinary food or water products simply cannot impact this process. Now, the theory actually states that acid foods cause the body to pull calcium out of the bones in order to maintain the normal blood pH. However, what we know from a 2009 meta-analysis is that there was no association between the body's calcium levels and urine calcium levels. What they did find was that if your FOOD has higher calcium levels, so will your urine... which makes logical sense. So just to recap, higher acidic foods do not appear to pull calcium from your bones. If you want to dive deeper into this topic, I'd suggest checking out this article.

If you'd like to learn more about hydration for athletes or connect with Dr. Molloy, you can visit M2 Performance Nutrition's Website, and follow them on Instagram.

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