Hydration on the Run

By Holley Samuel MEd, RD, LD, CSSD, 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 are sweating in their workouts and 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 they 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. 



Water

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 and as much as 50-80oz on the hottest days. How much we sweat varies 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: To understand your unique sweat rate, weigh yourself without clothes before you go out for a run. Then run for 60 minutes, keeping track of any and how much water you drink or if you use the bathroom. Then weigh yourself immediately after you finish your run without clothes. If you want to calculate your unique sweat rate, visit this calculator and enter the data you collected from this mini-experiment. 

The goal is 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 activity, and dehydration negatively impacts your overall health too. 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 1 gulp to make running math easier! On hotter days, you’ll likely have to drink more water more frequently. 

Electrolytes

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. Electrolytes help us maintain fluid balance, which helps our muscles contract and relax. 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 maintain your performance and also keep you safe and healthy.

When we consume water only or not enough electrolyte, 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, but also notes that athletes with saltier sweat may need up to 1200mg of sodium per hour. Research also 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 sport performance research centers, but there are new products being released like the the HDrop, Nix Sensor, or Precision Hydration sweat composition tests 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

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.  On hotter days or for saltier sweaters, make all your fluids sports drink or electrolytes.

  • 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. 

  • Find a vessel you can use to carry your hydration like a handheld water bottle, hydration vest, or practice stashing bottles on 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.

    • My favorite handhelds: 20oz & 18oz soft flask

Keep sweating and stay hydrated this summer!

 

References

Belval LN, Hosokawa Y, Casa DJ, Adams WM, Armstrong LE, Baker LB, Burke L, Cheuvront S, Chiampas G, González-Alonso J, Huggins RA, Kavouras SA, Lee EC, McDermott BP, Miller K, Schlader Z, Sims S, Stearns RL, Troyanos C, Wingo J. Practical Hydration Solutions for Sports. Nutrients. 2019 Jul 9;11(7):1550. doi: 10.3390/nu11071550. PMID: 31324008; PMCID: PMC6682880.

Sims ST, Rehrer NJ, Bell ML, Cotter JD. Preexercise sodium loading aids fluid balance and endurance for women exercising in the heat. J Appl Physiol (1985). 2007 Aug;103(2):534-41. doi: 10.1152/japplphysiol.01203.2006. Epub 2007 Apr 26. PMID: 17463297.

Sims ST, van Vliet L, Cotter JD, Rehrer NJ. Sodium loading aids fluid balance and reduces physiological strain of trained men exercising in the heat. Med Sci Sports Exerc. 2007 Jan;39(1):123-30. doi: 10.1249/01.mss.0000241639.97972.4a. PMID: 17218894.

Vitale, K., & Getzin, A. (2019, June 7). Nutrition and Supplement Update for the Endurance Athlete: Review and Recommendations. Retrieved April 22, 2020, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6628334/

Von Duvillard SP, Braun WA, Markofski M, Beneke R, Leithäuser R. Fluids and hydration in prolonged endurance performance. Nutrition. 2004 Jul-Aug;20(7-8):651-6. doi: 10.1016/j.nut.2004.04.011. PMID: 15212747.

Holley Samuelrunning nutrition, marathon training, running, athlete