Chronic Changes in Body Water across Days
Athletes and laborers should avoid beginning a training session or competition with a body water deficit that originated on the previous day. However, it is difficult to know how much fluid is needed, if any, unless accurate body- weight measurements are taken at the same time each day such as in the morning after waking, while wearing the same clothing. It also is wise to use a sensitive digital scale that employs a strain gauge, not a spring mechanism, to measure body weight. If day-to-day changes in body water are detected, corrective steps should be taken that are dictated by the extent of the hypohydration. For example, athletes reporting to a training session – lighter than on the previous day should rehydrate prior to exercising, by following the preexercise recommendations of the ACSM see the bulleted list on pageAthletes reporting with a – body-weight weight deficit should reduce training intensity and duration that day and concentrate on replacing lost fluids. If the body-weight deficit is or more, the athlete should consult with a sports medicine physician for a medical examination and consultation.
Urine An Index of Fluid Balance
The kidneys regulate fluid and electrolyte balance very accurately from one day to the next. Even though strenuous, prolonged exercise -might result in large sweat losses, the balance of water and salt is restored within hours, for most athletes, if they consume a normal diet. This is regulated by two hormones: aldosterone, which controls sodium and chloride balance, and AVP arginine vasopressin, also known as ADH, or antidiuretic hormone, which controls water balance. Unless sweating causes a loss of body water that exceeds of body weight, aldosterone and AVP regulate wholebody fluid and electrolyte balance within of normal levels, on any given day.
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Knowing this, it is reasonable to expect the properties of urine to reflect body water status. That is, urine should be concentrated and scanty when the body is dehydrated and is conserving water. The opposite ought to be true as well; urine should be dilute and plentiful when a temporary excess of body water exists. Indeed, this is precisely what occurs. For example, the average adult excretes approximatelyL each day. If your urine volume is less than L during any period, your body is conserving water via the hormone AVP. This is a sign that you should consume extra fluids during and between meals. This also explains why nutritionists and exercise physiologists recommend checking urine volume as one means of determining hydration status.
Relevant laboratory techniques that analyze urine properties include measuring either osmolality or specific gravity. Osmolality refers to the concentration of a sample and is affected by all dissolved particles in a standardized volume mass of fluid. Measurements of osmolality require a sophisticated instrument, a trained laboratory technician, and are time-consuming. Specific gravity refers to the density mass per volume of a urine sample in comparison to pure water. Any fluid that is denser than water has a specific gravity greater than and normal urine specimens usually range fromtoin healthy adults. During dehydration or hypohydration, urine specific gravity exceeds When excess water exists, values fromtoare typically seen. Specific gravity can be measured quickly and accurately with a handheld device known as a refractometer, shown in figure First, one or two drops of a urine specimen are placed on the stage of the refractometer see figure .a. Next, this instrument is held up to a bright light, which passes through the specimen and through a lens, causing the specific gravity to appear on a scale that ranges fromtofigure .b. Due to its ease of operation, this device can be used indoors or outdoors. Available from scientific supply companies, the
Use of a refractometer to measure urine specific gravity. cost of inexpensive models begins at $. Despite its relative ease of use, purchasing and using a refractometer still may be too intimidating for the average athlete. Urine Color
In an attempt to simplify the analysis of urine, with a method that all athletes might use, our research team has conducted a series of experiments involving the color of urine Ucol. We reasoned that if Ucol were directly proportional to the level of dehydration, virtually anyone could determine when they need to rehydrate. We began by developing a Ucol scale that could be used to derive a number or rating. This color scale was based on previous observations of urine samples, collected in field and laboratory studies of soldiers, dating back toand was printed on a laminated chart. Since publishing our findings regarding this Ucol scale inwe have had numerous requests from nutritionists, coaches, and physiologists around the world. Your copy appears on the rear cover of this book. As you can see, the eight-color scale includes colors ranging from very pale yellow number to brownish green number .