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In humans, electrolytes play a vital role in various physiological processes. Balancing electrolyte levels is essential for normal body functions; their imbalance can be life-threatening. The major electrolytes include sodium, potassium, chloride, calcium, phosphate, and bicarbonate. They are primarily involved in physiological processes, such as nerve signal transmission, membrane trafficking, muscle contraction, buffering body fluids, and balancing water levels in the body.
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The hydration of cement is an exothermic reaction in which heat is generated as cement hydrates. This heat of hydration is critical to cement's strength development. The rate at which this heat is generated affects the temperature rise, with a majority of the heat being released early in the hydration process, half within the first three days, and about 75% within the first week.
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Substances that undergo either a physical or a chemical change in solution to yield ions that can conduct electricity are called electrolytes. If a substance yields ions in solution, that is, if the compound undergoes 100% dissociation, then the substance is a strong electrolyte. Complete dissociation is indicated by a single forward arrow. For example, water-soluble ionic compounds like sodium chloride dissociate into sodium cations and chloride anions in aqueous solution.
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Water functions as a solvent accommodating various solutes, which can be categorized under electrolytes and non-electrolytes. Non-electrolytes are usually held together by covalent bonds, restricting them from dissociating in solution, thereby leading to a lack of electrically charged components upon dissolving in water. They are predominantly organic molecules, such as glucose, creatinine, and urea. Electrolytes, on the other hand, are compounds that can break down into ions in water.
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The kidneys concentrate or dilute urine to maintain water and electrolyte balance. Nephrons, particularly the loop of Henle, play a crucial role in this process through the countercurrent multiplication system. This system establishes a high osmolarity in the renal medulla, which is essential for water reabsorption. In the loop of Henle’s descending limb, water is reabsorbed into the surrounding medulla due to its permeability to water. In contrast, the ascending limb actively transports...
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Interindividual variability in sweat electrolyte concentration in marathoners.

Beatriz Lara1, César Gallo-Salazar1, Carlos Puente1

  • 1Camilo José Cela University Exercise Physiology Laboratory, C/ Castillo de Alarcon, 49, Villafranca del Castillo, 28692 Spain.

Journal of the International Society of Sports Nutrition
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Summary

Marathon runners show significant variability in sweat sodium and chloride concentrations, with 20% experiencing high losses. These electrolyte needs are influenced by sex and running pace, not other personal factors.

Keywords:
AthletesExerciseFluid balanceHyponatremiaOsmolalitySex

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Area of Science:

  • Exercise Physiology
  • Sports Nutrition
  • Human Physiology

Background:

  • Sodium intake during exercise is crucial for endurance athletes to prevent electrolyte imbalances.
  • Individual sweat electrolyte concentrations vary significantly, impacting hydration and nutrition strategies.
  • Understanding sweat electrolyte loss is vital for optimizing performance and health in marathon runners.

Purpose of the Study:

  • To determine the sweat electrolyte concentration in a large cohort of marathon runners.
  • To investigate the inter-individual variability of sweat sodium (Na(+)), chloride (Cl(-)), and potassium (K(+)) concentrations.
  • To identify factors influencing sweat electrolyte concentration in marathon runners.

Main Methods:

  • 157 experienced marathon runners (141 male, 16 female) provided sweat samples during a marathon race using sweat patches.
  • Sweat samples were collected under race conditions (24.4°C, 27.7% humidity).
  • Sweat electrolyte concentrations (Na(+), Cl(-), K(+)) were measured using photoelectric flame photometry.

Main Results:

  • Mean sweat Na(+) concentration was 42.9 ± 18.7 mmol·L⁻¹, Cl(-) was 32.2 ± 15.6 mmol·L⁻¹, and K(+) was 6.0 ± 0.9 mmol·L⁻¹.
  • Women exhibited significantly lower sweat Na(+) and Cl(-) concentrations compared to men.
  • 20% of runners had high sweat Na(+) concentrations (>60 mmol·L⁻¹), with no female runners reaching this level.

Conclusions:

  • Inter-individual variability in sweat electrolyte concentration is substantial and not explained by factors like age, body characteristics, or training.
  • Sex and running pace were identified as factors influencing sweat electrolyte concentrations.
  • A significant portion of marathoners may require individualized sodium intake recommendations due to high sweat salt losses.