Is it Okay to Weigh Athletes for Hydration Purposes? Q&A With RD Rebecca McConville
Rebecca McConville MS RD LD CSSD CEDRD-C is a sports dietitian, eating disorder specialist, and author of Finding Your Sweet Spot- How to Avoid REDs. Becca has a passion to take complex concepts like REDS and make it relatable. She has a REDs informed provider certification program and co-leads with MBE an annual Eating Disorder in Sport workshop.
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RM: Hydration can be one of the most overlooked yet impactful components of athletic performance. Unfortunately, body weight is often used to determine hydration needs. However, we don’t need to step on a scale to determine if we are adequately hydrating. There are other methods to gauge fluid losses during activity without involving weight.
Measuring body weight has been a popular method to “guesstimate” one’s hydration status. By weighing an athlete before and after training and subtracting their fluid consumption (oz) during training, we can estimate what that athlete’s hydration needs would be per hour to maintain adequate hydration. The theory is that the weight change that occurred during training correlates with the amount of sweat loss that occurred. We can then determine a target amount of fluid consumption that would compensate for those losses. However, this is not a very accurate method to determine hydration needs. Many uncontrollable, unpredictable factors affect weight, making it a measurement that is actually quite volatile.
Additionally, and most importantly, reliance on weight can be triggering and anxiety-provoking for many athletes.
For example, those who have a history of eating disorders may have come to attach much of their self-worth to the number on the scale. It then would seem counterproductive to endorse a practice that puts an overemphasis on weight changes, especially when that practice has a high error rate.
Here are 5 ways to determine hydration without ever stepping on the scale:
- Use a urine chart to gauge the color of your pee throughout the day. Here is a printable pdf by Gatorade.
- You may also use how often you are urinating as a marker. You should be voiding 4-6 times a day and generally within the hour after training when properly rehydrating.
- A more sensitive yet invasive measurement is urine specific gravity (USG). USG measures the concentration of particles in urine and the density of urine compared with the density of water. Another option is MX3, which functions similarly by testing salivary osmolarity (SOSM).
- Sweat tests help determine the electrolyte composition of sweat. While these previous tests assess for volume of fluid loss, sweat tests measure sodium & electrolyte loss, a factor that impacts overall hydration.
- Start with basic guidelines then go from there. These guidelines will vary depending on weather temperature, humidity, heat adaptation, and personal experience. To keep these simple we will focus on total fluid consumed and not electrolytes.
- Before training consume ~ 16-20 oz
- During training consume ~ 6-12 oz every 20 minutes
- Afterwards consume ~ 2448 oz within 2 hours of completion
With time and unbiased experimentation, the body will let us know how much fluid we need, when we need it, and what personal factors most impact our hydration status. No number on a scale can provide that roadmap.
REFERENCES:
O’Neal E, Boy T, Davis B, Pritchett K, Pritchett R, Nepocatych S, Black K. Post-Exercise Sweat Loss Estimation Accuracy of Athletes and Physically Active Adults: A Review. Sports (Basel). 2020 Aug 11;8(8):113. doi: 10.3390/sports8080113.
https://www.gssiweb.org/sports-science-exchange/article/sse-97-hydration-assessment-of-athletes
Smeltzer SC, et al. Brunner & Suddarth’s Textbook of Medical-Surgical Nursing, 11th edition. Lippincott Williams & Wilkins, 2007.
Brown HA, Clark B, Périard JD. Reliability and validity of the MX3 portable sweat sodium analyser during exercise in warm conditions. Eur J Appl Physiol. 2024 Jul;124(7):2153-2160. doi: 10.1007/s00421-024-05447-w. Epub 2024 Mar 2.
