Dehydration is a condition in which the body loses more fluids than what is taken in. This is of particular concern during exercise as dehydration impairs physiologic and cognitive function, increases the risk of heat illness, and decreases exercise performance. Show Exercise results in heat production that the body balances through conduction, convection, evaporation, and radiation. Heat dissipation through sweat evaporation is the primary mechanism in which the body cools itself during exercise in most sports. However, there are large differences between sport types.
ASSESSMENT There are primarily three practical field assessment methods used to assess hydration status in athletic populations: body weight change, urine color, and urine specific gravity (USG). Body Weight Change In order to assess hydration status via body weight changes, normal baseline body weight must be known. This can be determined by measuring body weight for three consecutive days (with daily variability of 0.51 ± 0.2 kg). Best practices for this include standardized clothing, measuring on the same scale, and taking measurements at the same time of day. Euhydration, or well-hydrated status, can be determined if an individual’s body weight is within ±1% of the baseline value. Urine Color Urine color can also be used to monitor hydration status throughout the day. Urine color should be maintained at “pale yellow” or “straw-colored” for euhydration. A urine color chart for comparison has been developed and validated by Armstrong and colleagues (Armstrong et al., 1994). Urine color should be assessed midstream and environmental lighting should also be taken into consideration when using urine color to assess hydration status. It is also important to note that clear urine is not the goal for hydration as this may indicate overhydration, increasing the risk for hyponatremia which can have potentially fatal consequences. Urine Specific Gravity Urine-specific gravity is a less subjective method to quickly assess pre-exercise hydration status, however, a refractometer is required. Refractometers are simple to use and some are somewhat inexpensive. USG values <1.020 g/mL-1 indicate euhydration. The best practice is to test the first-morning urine when possible as it is the most accurate reflection of hydration status. This may pose logistical obstacles such as early morning practice times, athletes voiding urine before arriving at facilities, or lack of resources and space to store urine samples during the measuring. EDUCATION Hydration Before Exercise The goal of fluid intake before exercise is to start activity hydrated with normal electrolyte levels. For example, fluid intake of 16-20 fl. oz. 2 hours before exercise should ensure proper hydration. Hydrating early should be another consideration to allow for urine output to return to normal before exercise. However, hyperhydration, or over-hydrating, is not recommended due to unclear benefits and the risk of dilutional hyponatremia. Hydration During Exercise The goal of fluid intake during exercise is to prevent excessive dehydration, indicated by >2% body weight loss from water deficit. Fluid needs during activity are highly individualized and dependent on sweat rates, exercise duration, and opportunities to drink. It is recommended to monitor body weight changes during training and competition to estimate sweat rates for fluid replacement. As a starting guideline, 7-10 fl. oz. every 15-20 minutes may be sufficient for some individuals. However, events with longer durations or different environmental conditions may necessitate different fluid replacement protocols. Therefore, fluid replacement during exercise should be determined on an individual basis. Hydration After Exercise After exercise, the goal is to correct any fluid deficits that occurred during activity. For events with long recovery periods (>24 hours), drinking fluids and consuming foods with sodium is generally sufficient to achieve rehydration. During periods of rapid recovery (<24 hours) or in response to substantial fluid loss, ingestion of 1.5 L/kg (23 fl. oz./lb) of body weight lost is often acceptable to achieve complete rehydration. The additional 0.5 L volume should be included to offset increased urine production during rapid rehydration. These fluids should be consumed over several hours when possible to allow for proper fluid retention. If recovery periods are even shorter (<12 hours), then more aggressive rehydration plans may be warranted. » ALSO SEE: Ashley Labrador — 2021 Most Valuable HS Athletic Trainer of the Year ADDITIONAL CONSIDERATIONS Fluid Types Other beverages besides water can also be good choices to hydrate such as sports beverages, fruit juice, milk, and tea. Palatability of fluids can help promote fluid consumption. Therefore, flavor, temperature, and sodium content should also be considered with athlete preferences to promote good hydration habits. To learn more about sports nutrition and CPSDA, go to www.sportsrd.org. Written by a Collegiate and Professional Sports Dietitians Association Registered Dietitian (RD). How is sweat loss measured?Your standard sweat check procedure is:
Check/measure the amount of fluid consumed during training. Add the amount of fluid lost to the amount of fluid consumed to get total fluid losses. Divide the total amount of fluid lost by the number of hours of training to get fluid losses per hour.
How do you estimate the sweating rate of the athlete?Formula for Calculating Sweat Rate
Calculate each athlete's sweat rate (sweating rate = pre-exercise body weight - post-exercise body weight + fluid intake - urine volume/exercise time in hours) for a representative range of environmental conditions, practices, and competitions.
How would a practitioner determine total sweat fluid losses?Although there is currently no gold-standard method to measure hydration status or whole-body sweating rate, the simplest and most accurate assessment is via mass balance (Armstrong, 2007). That is, the acute change in body mass from before to after exercise can be used to calculate thermoregulatory sweat losses.
What is a sweat test for athletes?Sweat testing seeks to help athletes tailor their own fluid and sodium intake parameters by establishing two key factors: your sweat rate (i.e., how much fluid you lose per hour) and sweat sodium concentration (i.e., the amount of sodium you lose in your sweat).
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Individual body weight should be monitored to estimate sweat loss to prevent a body weight loss of
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