Electrolytes are widely associated with hydration and exercise. This guide explores the science behind electrolyte minerals, their roles in the body and the practical factors to consider when choosing an electrolyte product.
What are electrolytes?
Electrolytes are essential minerals that carry an electrical charge in the body's fluids, including blood, sweat and intracellular fluid. The primary electrolytes include sodium, potassium, magnesium, calcium and chloride.
They contribute to physiological processes including fluid balance, nerve signalling, muscle contraction and acid-base balance, although the specific role varies between electrolytes.
Because the body cannot make these minerals, they must be obtained through food and drink. During exercise, heat exposure or periods of heavy sweating, the body can lose both water and electrolytes through sweat.
Why hydration is more than water
Hydration involves both fluid intake and the body's regulation of fluid balance. Sweat contains water and electrolytes, particularly sodium and chloride, although the amount lost varies between individuals and circumstances.
During prolonged exercise or heat exposure, fluid intake should be proportionate to losses, as excessive water consumption can dilute blood sodium concentrations. Guidance from the American College of Sports Medicine therefore supports individualised fluid and electrolyte planning, particularly during activity involving substantial sweat losses.1
Hydration is personal.
The sodium-potassium pump
At cellular level, the sodium-potassium pump helps maintain different concentrations of sodium and potassium across cell membranes. Using energy from ATP, it typically transports three sodium ions out of the cell and two potassium ions into the cell during each cycle.
This active transport helps maintain electrochemical gradients across cell membranes and supports the electrical activity involved in nerve impulses, muscle contraction and normal cardiac rhythm.
Electrolytes lost through sweat
Sweat composition varies widely between individuals, but sodium is the primary electrolyte lost. Sweat rate and sodium concentration are influenced by temperature, exercise intensity, genetics and heat acclimation.
Research reports substantial variation in sweating rate and sweat sodium concentration between athletes, reinforcing the need for individualised hydration strategies.3
Some athletes are naturally salty sweaters. White salt marks on clothing or skin after exercise can indicate higher sodium losses, while hot and humid conditions can increase sweat rate and therefore total electrolyte loss.
The five essential electrolytes
Sodium Na+
The principal positively charged ion in extracellular fluid and the primary electrolyte lost through sweat.
Chloride Cl-
Found alongside sodium in body fluids, lost through sweat and used as a component of stomach acid.
Potassium K+
Contributes to normal muscle function, nervous-system function and the maintenance of normal blood pressure.4
Magnesium Mg2+
Contributes to electrolyte balance, normal energy-yielding metabolism, muscle function and the reduction of tiredness and fatigue.5
Calcium Ca2+
Contributes to normal muscle function and neurotransmission and is needed for the maintenance of normal bones.6
Electrolytes and physical performance
Electrolyte losses can become more substantial during prolonged exercise, particularly when sweat rates are high. Fluid and electrolyte intake may be considered in relation to:
- Exercise duration and intensity
- Individual sweat rate
- Sweat sodium concentration
- Temperature and humidity
- Fluid and dietary intake
As exercise duration and sweat losses increase, these considerations can become more relevant. This particularly applies to endurance events, exercise in hot environments and repeated training sessions with limited recovery time.2
When might you need electrolytes?
Electrolyte losses may be greater during:
- Prolonged exercise involving substantial sweating
- Exercise in hot environments
- Activities associated with high individual sweat rates
- Multiple training sessions with limited recovery time
- Extended periods of physical activity
Daily needs vary considerably. Body size, training load, climate, diet and sweat rate all influence individual requirements.
A practical hydration strategy
- Start exercise adequately hydrated.
- Match fluid intake to individual needs.
- Consider sweat rate, exercise duration and environmental conditions.
- Account for sodium losses during prolonged or heavy sweating.
- Avoid excessive fluid intake.
- Refine your approach using experience from training sessions.
There is no one-size-fits-all approach. For shorter or lower-intensity sessions, water may be sufficient. During prolonged activity involving substantial sweating, both fluid and electrolyte intake may require consideration.
Key takeaways
- Electrolytes are charged minerals involved in numerous physiological processes.
- Sweat contains water and electrolytes, particularly sodium and chloride.
- Losses vary with sweat rate, sweat composition, activity and environmental conditions.
- During prolonged activity involving substantial sweating, both fluid and electrolyte intake may need consideration.
- Hydration requirements vary, so there is no universal approach.
References
- Sawka, M. N., Burke, L. M., Eichner, E. R., et al. (2007). American College of Sports Medicine position stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39(2), 377-390.
- Shirreffs, S. M., & Sawka, M. N. (2011). Fluid and electrolyte needs for training, competition and recovery. Journal of Sports Sciences, 29(Suppl. 1), S39-S46.
- Baker, L. B. (2017). Sweating rate and sweat sodium concentration in athletes. Sports Medicine, 47(Suppl. 1), 111-128.
- National Institutes of Health, Office of Dietary Supplements: Potassium Fact Sheet for Health Professionals.
- National Institutes of Health, Office of Dietary Supplements: Magnesium Fact Sheet for Health Professionals.
- National Institutes of Health, Office of Dietary Supplements: Calcium Fact Sheet for Health Professionals.
