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Preventative Hydration Protocols for Heat Stress Management: Applications from Sport Science
Normative Sweat Dynamics in Athletes
The amount of water and electrolytes (primarily sodium, Na+) lost due to thermoregulatory sweating during exercise can vary considerably within and among athletes. Even for the same individual, losses can vary greatly day to day. The reported range in sweating rate and sweat Na+ concentration ([Na+]) is ~0.5 to 2.0 L/h and ~10-90 mmol/L, respectively. Extrapolated for workers throughout a workday, this could result in multiple U.S. gallons of fluid lost in a day on the high end.
Effects of Dehydration
Proper hydration is essential, as even mild dehydration can decrease physical performance by 2-3 percent and cognitive performance by up to 10 percent.
Dehydration elevates core temperature responses and negates the thermoregulatory advantages conferred by heat acclimatization. When dehydrated, similar core temperature responses were observed for both unacclimated and acclimated states.
The capacity to perform high-intensity exercise, which results in exhaustion within a few minutes, is reduced by as much as 45 percent by prior dehydration corresponding to a loss of only 2.5 percent of body weight.
Exercise performance is impaired when an individual is dehydrated by as little as 2 percent of body weight. Losses of more than 5 percent of body weight can decrease the capacity for work by about 30 percent.
Fluid & Electrolyte Replenishment Guidelines
Appropriate fluid intake before, during and after exercise is important for health and optimal performance. Before exercise, athletes may achieve euhydration prior to exercise by consuming a fluid volume equivalent to 5–10 ml/kg BW (∼2–4 ml/lb) in the two to four hours before exercise to achieve urine that is pale yellow while allowing for sufficient time for excess fluid to be voided. Sodium consumed in pre-exercise fluids and foods may help with fluid retention. Drinking during exercise aims to address sweat losses that occur to assist thermoregulation. After exercise, the fluid should be restored by drinking a volume of fluid that is equivalent to ∼125-150 percent of the remaining fluid deficit (e.g., 1.25–1.5 L fluid for every 1 kg BW lost).
This article originally appeared in the September 2024 issue of Occupational Health & Safety.