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Does drinking plenty of water and a pinch of sodium before exercise help sustain your performance? This concept — called “pre-exercise hyperhydration” — is gaining attention in the world of sports, but is there any scientific evidence to back this approach?

Pre-exercise hyperhydration is all about increasing your body’s water levels before you hit the gym or start a physical activity. But it’s not as simple as just drinking a bunch of water. If you do that, you’ll probably find yourself making frequent trips to the bathroom and messing with your body’s release of anti-diuretic hormone, which impacts your blood pressure among other physiologic changes.

Instead nutritional aids, such as glycerol and sodium, are being investigated for their ability to increase total body water prior to exercise. Now, a new review published in Sports Medicine delves into the existing literature to unveil the potential impact of pre-exercise hyperhydration on performance, key physiological responses, and gastrointestinal symptoms.

The review included 33 studies and 403 participants (mostly males). Only a handful of the studies reported improvement in some exercise performance metric. Take a look at the nine studies that measured time-trial performance. Only two of them showed improvements after hyperhydration. However, hyperhydration may improve exercise capacity during “constant work rate exercises,” or physical activity performed at a consistent intensity for a set duration of time. Five of the seven studies looking at this metric did find that hyperhydration increased the time to exhaustion. This improvement is attributed to a reduction in heart rate and core body temperature, likely due to an increase in blood volume, specifically the plasma portion that carries water, salts, and enzymes.

There’s still much to learn about hyperhydration. What is the ideal combination of various osmotic aids (e.g., sodium, glycerol) to enhance fluid retention? How does hyperhydration impact women? For example, glycerol hyperhydration may not work the same for women at different times of their menstrual cycle. This is because the hormones estradiol and progesterone, which change throughout the cycle, can influence fluid balance in women.

And what about gastrointestinal issues? More than half the studies included in the review found hyperhydration increased the incidence of nausea, diarrhea, vomiting, and other gastrointestinal problems. But there was variability in how these symptoms were tracked. So the review calls for future research to adopt robust methods in assessing gastrointestinal symptoms to understand better the relationship between these symptoms and hyperhydrating. There is also a need to investigate the effects of hyperhydration across different exercise modalities.

To learn more, read the publication in Sports Medicine.

This work is part of the Wu Tsai Female Athlete Program at Boston Children’s. The program is an innovation hub for the Wu Tsai Human Performance Alliance. Co-authors include William T. Jardine, Brad Aisbett, Monica K. Kelly, Louise M. Burke, Megan L. Ross, Dominique Condo, Julien D. Périard & Amelia J. Carr.

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