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What is it?

  • Electrolyte replacement supplements are powders, tablets or ready to drink products designed for replacement of fluid and electrolytes (in particular, sodium and potassium) lost through sweat or other body fluids. Typical uses include:
    • As a method of increasing total body water and plasma volume prior to exercise in hot environments, when opportunities for fluid replacement are inadequate to prevent significant fluid losses (pre-exercise hyperhydration).
    • As an alternative to standard sports drinks when it is deemed of value to replace large electrolyte losses during and after exercise with a more aggressive approach, or where electrolyte replacement is desired with limited or no carbohydrate intake.
    • To restore fluid/electrolyte deficits caused by other factors such as the dehydration techniques undertaken to “make weight” for competition or gastrointestinal upsets (vomiting/diarrhea etc.).
  • Guidelines around the need, or optimal plan, for sodium intake during endurance (i.e. > 1 hour) and ultra-endurance exercise (i.e. >4 h) are unclear.
    • General recommendations include 0.5–0.7 g per litre of fluid (21–30 mmol/L)1 with this target being set as a balance between preserving thirst drive and preserving the palatability of fluids.
    • There are suggestions that in situations of large sweat sodium losses (e.g. ultra-endurance exercise, individuals who have “salty” sweat or combination of these factors) a more proactive approach to sodium intake during exercise may be needed. However, the best method for assessing these needs, and planning for sodium replacement, are yet to be determined.
  • Two contentious issues around electrolyte/sodium replacement during exercise concern the prevention of cramps and hyponatremia.
  • Exercise associated muscle cramps may be caused by multiple factors, with primary risk factors including fatigue due to unaccustomed volume/intensity of exercise and previous history of cramps. There is some evidence, although controversial2 that whole body sodium depletion may be a cause of specific types of cramps in some individuals. Electrolyte supplementation may be beneficial in these athletes.3 There is also some suggestion that a sudden drop in plasma sodium concentration (e.g. dilution due to large, sudden intake of plain water) may increase susceptibility to muscle cramps, although the exact mechanism underlying this effect has not yet been determined.4
  • Typically, plasma sodium concentrations are typically tightly regulated at ~ 135–145 mmol/L and athletes become mildly hypernatremic (high blood sodium concentrations) during exercise because sweat losses deplete fluid stores at a higher rate than sodium/electrolyte losses (sweat is hypotonic compared with blood).
    • Mild hyponatremia (<135 mmol/L) can occur in some sports, often without overt symptoms, due to the strategies used to replace sweat fluid and sodium losses. An athlete can dilute blood sodium concentrations during exercise by drinking fluids at a rate that is slightly greater than their sweat losses, or by replacing large sweat losses (and the accompanying large electrolyte loss) with low sodium fluids (e.g. water or soft drinks). Sodium replacement during exercise can address this issue provided the total fluid consumed remains less than sweat losses. Whilst mild hyponatremia is usually asymptomatic, a large and sudden drop in blood sodium concentration, even when the final value remains > 130 mmol/L, can result in symptoms of severe hyponatremia (below), due to the rapid shift of water into the intracellular space (Hew Butler et al. 2015).
    • Severe hyponatremia (plasma sodium < 130 mmol/L) can be associated with confusion, nausea, headaches, and the potentially fatal outcome of cerebral oedema. It is comparatively rare in sport and occurs when an athlete consumes fluid at a rate that is substantially higher than actual sweat losses, and the rate of urine production. This condition may be exacerbated in individuals/scenarios involving inappropriate secretion of the renal hormone ADH (also known as vasopressin) which reduce urine production (vasopressin or ADH). Although sodium replacement in concert with “over drinking” behaviour may slightly reduce the degree to which hyponatremia develops, the underpinning cause of severe hyponatremia is excessive fluid intake and should be tackled directly.5
    • Rehydration after exercise (or other dehydrating events) requires the replacement of electrolyte losses before fluid balance can be fully restored. In the absence of electrolyte replacement, fluid replacement will restore blood osmolarity (concentration) before it has replaced its volume, leading to a reduction in thirst and increased urination. Such signs can be confused with adequate or overhydration. Rehydration after the development of moderate-severe dehydration (e.g. fluid loss > loss of 2% BM) is more efficient when there is a considered replacement of electrolytes. Although sodium can be replaced by eating salty foods (e.g. bread, breakfast cereal, cheese & crackers, VegemiteTM) or adding salt to meals, electrolyte supplements or sports drinks with higher sodium content can be useful for rapidly restoring fluids and electrolytes with a more targeted approach, especially if food intake is likely to be minimal or delayed after exercise. See Table 1 for details on higher sodium foods.

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