Page 91 - JSOM Spring 2023

of sodium (460–1,150mg/qt) are most effective for ensuring and dark yellow or smelly urine often indicates dehydration
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adequate hydration status before exercise. Sodium can also be (Figure 1). However, urine color may be altered if certain B
ingested from food. vitamins, namely riboflavin, are being taken in large amounts.
Likewise, eating beets may cause the urine to appear brown
During physical activity, Operators should aim to replace fluids or dark red.
at a rate that would prevent losing more than 2% of their body
weight. Practically, this translates into 16–32 fl oz per hour.
1,4
Most will find that consuming fluids at regular intervals (i.e.,
4–8 fl oz every 15 minutes) is better tolerated than drinking FIGURE 1 Urine
all fluids at one time. However, each Operator should monitor color chart.
his or her own fluid losses because these general recommenda-
tions do not account for individual differences. Some will be This chart can be
very heavy sweaters, and others may be heavy salt sweaters. used to rapidly
assess hydration
Sweat rates have been reported to vary from 0.16 to 5.73L per status. Urine capture
hour, depending on age, type of activity, physical fitness, ac- should occur in a
climation status, clothing, and, of course, environmental con- clear or white cup.
ditions. Further, for sustained physical activity lasting more
1,8
than one hour, a combination of fluid, electrolytes, and car- Image created by
Human Perfor-
1,4
bohydrates (e.g., sports drinks) should be considered. Fluid mance Resources by
intakes should not exceed 48 fl oz per hour. Table 1 provides CHAMP (HPRC)
criteria to consider when selecting a sports drink. at the Uniformed
Services University,
Bethesda, MD.
TABLE 1 Criteria for Sports Drinks 1
Ingredient Amount per 8 fl oz
Sodium 82–163mg
Potassium 16–46mg Electrolyte Monitoring
Carbohydrate 12–24g
Electrolyte (e.g., sodium, potassium, chloride) and mineral
After physical activity, fluid losses need to be replaced. Hy- (e.g., calcium, zinc, iron) losses from sweating can be substan-
dration status can be restored by consuming regular foods tial, with sodium losses ranging from 50–7,000mg/hr, with
and beverages. More specifically, if actual changes in body higher values noted in heavy sweaters and those unaccus-
1,4
weight are known, a one-pound loss in body weight would re- tomed to working in the heat. 10–12 Potassium losses may range
quire ingesting 16–24 fl oz of liquid to fully restore balance. from 25–2,000mg/hr. As such, commercial fluid replacement
1
1,4
Ideally, the fluid should contain sodium at a concentration of beverages typically provide sodium and potassium; some also
approximately 250mg per 8 fl oz to stimulate thirst and fluid provide magnesium and calcium as well, but the amounts typi-
retention, and promote a more rapid and complete recovery. cally are low. The recommended ranges for sodium and potas-
1,4
Sodium recommendations can also be met through food (e.g., sium to offset sweat losses and promote fluid absorption are
pretzels, crackers, soup, deli meat, jerky, etc.). Additional fluids 20–30mEq/L (460–700mg/L) and 2–10mEq/L (78–390mg/L),
should be incorporated throughout the day rather than con- respectively. Chloride is the only anion recommended as it
1
sumed in a short interval. Table 2 provides a summary of fluid optimizes fluid absorption. Importantly, loss of electrolytes
recommendations before, during, and active physical activity. cannot be estimated from changes in body weight.
Monitoring Hydration Special Populations

Hydration status is most easily monitored by changes in body Certain populations of warfighters are at risk for dehydration
weight, and a baseline measurement can be established by ob- due to tactical gear configurations, equipment and/or trans-
taining a first morning body weight over several days. Ideally, portation used, and mission types.
nude weight should be recorded both before and after phys-
ical activity to estimate fluids lost through sweating. In the Pilots/Aircrew/Parachutists
field, a refractometer can be used to measure urine specific One such population are aviators and aircrew who fly in tac-
gravity (USG), another indicator of hydration status. A USG tical aircraft and/or helicopters. Dehydration is commonly re-
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≤1.020 is desirable and reflects adequate hydration. Alterna- ported in aircrew populations and can be attributed to high
9
tively, urine color can subjectively assess hydration, in which operations tempo and difficulty with urination in flight. Air-
6
pale yellow, almost clear urine suggests adequate hydration, crew have been known to intentionally dehydrate themselves,
TABLE 2 Fluid Recommendations Before, During, and After Physical Activity
Pre-Physical Activity
Duration (2–4 hours prior) During Physical Activity Post-Physical Activity
<60 minutes 14–22-oz water (2–4mL/lb) Drink water to thirst 20–24 fl oz water per pound of body weight lost
≥60 minutes 14–22-oz water (2–4mL/lb) 16–32 fl oz per hour, adjust 20–24 fl oz water per pound of body weight lost.
carbohydrates and electrolytes based Additional fluids consumed throughout the day,
on environment and sweat rate; no combine with foods containing sodium; daily fluid
more than 48 fl oz per hour intake should not exceed 384 fl oz (12 qt) per day

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