Assessing Hydration Status
Our bodies are composed of 45 to 75 percent water, with variability due to fat and fat-free mass (fat mass is ~10 percent water, while fat-free mass is ~70 to 80 percent water), age, sex, and race (ACSM et al. 2007). Because of these differences, as well as inter- and intraindividual differences in sweat rate and other rates of water loss, there isn’t a single recommended amount of fluids that should be ingested in order to maintain euhydration.
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Measuring hydration status is best achieved by measuring body water fluctuations. There are precise assessments of hydration status that can be measured in the laboratory involving blood sample collections, but these are not practical for athletes in practice or competition settings. However, established field-tests and collection methods can be done in the athlete’s environment.
Simple biomarkers that athletes can use to assess hydration status include urine color and body weight, and while these markers have limitations when used independently, they have greater validity when used in conjunction with each other (Stachenfeld 2014). Athletes should be encouraged to routinely examine the color of their urine in the morning, and they can be provided a urine color chart with which to compare their observation. Athletes can also take their weight first thing in the morning, without clothes on and after having voided, as daily weight will change less than one percent unless affected by hydration status. Tracking several first morning weights (nude, after voiding) will help establish a baseline euhydration status with which they can compare future measurements (ACSM et al. 2007). While these measurements are not as precise as laboratory testing measurements, when taken together they can help an athlete assess one’s hydration status.
Athletes who have access to measuring their urine specific gravity (USG) utilizing specialized testing strips will have another method to assess hydration status. Many university and professional teams will regularly measure USG, especially during hot temperatures. A USG of <1.020 indicates euhydration, and values higher than this amount indicate the athlete is starting to become dehydrated and rehydration strategies should be implemented.
Put together, fluids are an essential component of any athlete’s sport nutrition plan. Athletes should be educated on the function of fluids in the body, have a basic understanding as to what their daily fluid needs are, and how to assess their hydration status.