Hydration For Running | What To Drink To Maximize Performance

Updated: Sep 25

By Holley Samuel MEd, RD, LD, CPT

With summer on the horizon, one of your biggest concerns as an endurance athlete is probably hydration. You may be wondering what to drink, how much, and when to drink it, along with how to know if you're hydrating well enough to achieve your goals. Whether it's summer or not, endurance athletes sweat during their workouts, and they're losing water and electrolytes. Our environmental conditions, along with more specific details like which phase we're in of the menstrual cycle, if we're female, can also impact how much we sweat and its composition.

Our bodies store carbohydrates as glycogen and body fat for energy, but we cannot store water and electrolytes in the same way. This is why we need to replace what we lose during our training or race. Once we become too dehydrated and start to experience symptoms like headache, fatigue, chills, cramping, or gastrointestinal distress, we can probably kiss our performance goals goodbye.

How Much Water Should I Drink When Running?

First, let's talk about the fluid component of your hydration strategy. On average, we lose about 12-32oz of fluid in sweat per hour or as much as 50-80oz on the hottest days. How much we sweat varies from person to person, independent of their environment. We don't need to replace 100% of what is lost in sweat, but aiming for at least 80% can help prevent significant impacts on performance.

Optional Mini Experiment

  1. Weigh yourself without clothes before going out for a run

  2. Run for 60 minutes and keep track of how much water you consume or if you use the bathroom

  3. Weigh yourself immediately after you finish your workout without clothes

  4. Use this calculator and enter the data you collected from this mini-experiment

The goal:

To prevent anything more than 2-3% body weight loss by replacing fluids and electrolytes during your activity.

*Studies show that performance is significantly impacted when we lose too much weight through sweat during training, and dehydration negatively impacts our overall health.

In order to meet your hydration needs, consuming between 4-8oz of water every 10-20 mins during activities is recommended, especially for activities that last longer than 60 minutes. Remember that 1oz is about one gulp to make running math easier! On hotter days, you'll likely have to drink more water more frequently.

Why Do I Need Electrolytes?

Electrolytes help us maintain fluid balance, which allows our muscles to contract and relax when training. Electrolytes include sodium, calcium, potassium, bicarbonate, magnesium, and chloride as the most notably lost in sweat, with sodium and potassium being the most significantly lost. Since running requires many muscles to contract and relax, including our heart, maintaining proper fluid balance through adequate electrolyte intake during exercise is vital to maintaining your performance and keeping you safe and healthy.

When we consume water only or not enough electrolytes, this can cause a condition called hyponatremia, which can be extremely dangerous or fatal as a result of improper fluid balance. Other common symptoms of dehydration or improper hydration (meaning you don't take in the correct ratio of electrolytes to fluid for your unique needs) include calf cramps, side stitches, gastrointestinal distress like vomiting and diarrhea, and muscle spasms that can also lead to injury.

The American College of Sports Medicine recommends between 300-600mg of sodium per hour during prolonged exercise and notes that athletes with saltier sweat may need up to 1200mg of sodium per hour.

Research indicates that sodium loading prior to competition intended to achieve the status of euhydration- or being optimally hydrated- leads to improved performance outcomes in both men and women.

You may be thinking about how the health industry encourages Americans to limit their sodium intake- while you should consult with your registered dietitian and physician about what applies to you individually, typically, athletes need far more sodium than the average person to replace what's lost daily in sweat.

Just like we all have different sweat loss rates, we also have different sweat compositions. Traditionally, it is challenging to assess your unique sweat composition without access to fancy equipment at university and sports performance research centers. Still, new products are being released like the Gatorade Patch that can help you assess and understand your sweat right at home.

For other electrolytes, meeting the recommended daily intake for athletes through daily diet should suffice, but as a dietitian, I typically recommend endurance athletes include between 100-200mg potassium and some magnesium and calcium in their hydration supplement during workouts longer than 90 minutes or on shorter workouts on hot days. Keep in mind that some forms of magnesium can cause gastrointestinal distress in those with sensitive guts, so it's best to look for magnesium citrate or chelated magnesium (otherwise known as magnesium bisglycinate) instead of magnesium oxide to avoid this.

How To Implement And How does this all come together?

  • Aim to drink 4-8oz water every 10-20 mins, especially on runs lasting longer than 60 minutes.

  • Alternate every other drinking interval with plain water and an electrolyte beverage to avoid potential gastrointestinal distress from taking too much at once.

  • While your running fuel like gels and chews may contain some electrolytes, read the labels and assess if you need an electrolyte supplement to meet the recommendation of taking 400-800mg sodium and 100-200mg potassium per hour.

  • My favorite brands are Skratch Labs, NUUN Podium series, Liquid IV, Stage Hydration, Elete, Ultima, Vitalyte, Generation UCAN Hydration, and Gatorade Endurance Formula.

  • Find a vessel you can use to carry your hydration like a handheld water bottle, hydration vest, or practice stashing bottles on the course, or doing a loop course around your car or home.

  • Practice with whatever you plan to use on race day to get your body accustomed to it ahead of time.


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