Hydration Beyond Water: Electrolytes, Performance, and What Actually Matters

Water usually suits shorter training sessions. Longer, sweatier exercise may need a personalised fluid and sodium plan, not simply more water. 1

Electrolyte roles

Sodium helps maintain fluid outside cells and supports nerve signalling and muscle contraction. Sweat losses make it particularly relevant during exercise. 1

Potassium is the main positively charged electrolyte inside cells. It supports cellular fluid balance, nerve transmission and muscle function, including the heart. Fruit, potatoes and legumes provide it. 2

Magnesium supports more than 300 enzyme systems, including energy production and muscle and nerve function. Sources include leafy greens, nuts, seeds, whole grains and dairy. 3

These essential functions do not prove that extra supplements improve performance. Kidney disease or medicines affecting potassium balance warrant clinical advice before supplementation. 2 3

Hyponatraemia risk

Exercise-associated hyponatraemia means low blood sodium during or after exercise. A major cause is drinking more fluid than the body can lose or excrete, sometimes alongside reduced water clearance by the kidneys. 4

Adding sodium does not make overdrinking safe. Sports drinks can also contribute to fluid overload. Responding to thirst rather than forcing fluids helps reduce risk. 4

Headache, nausea and vomiting can overlap with dehydration or heat illness. Stop exercising and seek prompt assessment if symptoms persist or worsen, especially after heavy drinking. Do not automatically treat them with more fluid. 4

Confusion, seizures or collapse during or after exercise need emergency assessment. In New Zealand, call 111 and ask for an ambulance. 4 5

Practical guidelines

For most sessions around an hour or less in moderate conditions, water and normal meals suffice. Heat, heavy sweating and repeated sessions change the picture; there is no automatic electrolyte deadline. 1

Sodium needs vary with sweat volume, sweat sodium and food intake. A single hourly dose cannot fit everyone. 1

Sports drinks combine fluid with carbohydrate, which can support performance when exercise requires additional fuel. A sugar-free electrolyte drink does not provide that same fuel. 6

Check sodium per prepared serving and the mixing volume. For example, 300 mg in 500 mL equals 600 mg per litre. This is label arithmetic, not a prescribed hourly target.

A pinch of salt and squeeze of citrus is not a measured replacement plan. Choose an approach you can quantify and practise during training.

Estimate your sweat rate

Weigh yourself before and after a representative session, using minimal dry clothing. Record drinks consumed, any urine passed and session duration. 1

Estimated sweat loss in litres = starting weight in kg minus finishing weight in kg, plus drinks in litres, minus urine in litres. Divide by hours exercised. 1

For example, losing 0.5 kg while drinking 0.5 litres over one hour, without urinating, suggests about 1 litre/hour of sweat loss. 1

Repeat in different conditions. This estimates fluid loss, not sweat sodium, and is not an instruction to force complete replacement during exercise. 1

Daily hydration

Australian and NZ reference intakes for drinks are 2.1 litres daily for adult women and 2.6 litres for adult men. These include other drinks, not just water; food supplies additional water. 7

These are population guides, not quotas. Exercise, heat, pregnancy and breastfeeding can increase needs. Follow an individually prescribed fluid limit rather than these general figures. 7

Pale-yellow urine is a rough guide. Interpret colour alongside thirst and usual patterns, not as a blood-sodium test. 1

For the wider post-training picture, see recovery nutrition. If you want help fitting hydration around your training, explore coaching.

References

1.McDermott BP, et al. National Athletic Trainers’ Association Position Statement: Fluid Replacement for the Physically Active. Journal of Athletic Training. 2017;52(9):877–895. doi:10.4085/1062-6050-52.9.02

2.National Institutes of Health, Office of Dietary Supplements. Potassium: Fact Sheet for Health Professionals. Source

3.National Institutes of Health, Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals. Source

4.Bennett BL, et al. Wilderness Medical Society Clinical Practice Guidelines for the Management of Exercise-Associated Hyponatremia: 2019 Update. Wilderness & Environmental Medicine. 2020;31(1):50–62. doi:10.1016/j.wem.2019.11.003

5.New Zealand Police. 111 Emergency Services. Source

6.Australian Institute of Sport. Sports drinks: What is it? Source

7.National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand: Water. Source

Quick answers

Do I need electrolytes for a one-hour gym session?

Usually not in moderate conditions. Water and normal meals generally suffice. Heavy sweating, prolonged training and repeated sessions may change your needs.

How much sodium should I take during long sessions?

There is no universal hourly dose. Sweat volume, sweat sodium and food intake matter. Check sodium per prepared serving rather than relying on a pinch of salt.

Can sports drinks prevent hyponatraemia?

Not if you overdrink. Their sodium cannot reliably offset excessive fluid intake. Avoid forcing fluids beyond your needs.

How much should I drink each day?

Australian and NZ adult references are 2.1 litres of drinks for women and 2.6 litres for men. These are guides, not quotas; activity, heat, pregnancy and breastfeeding change needs.

Do potassium and magnesium supplements improve hydration?

Their essential roles do not prove that extra supplements improve hydration. Prioritise varied foods, and seek clinical advice if deficiency or a relevant medical condition is suspected.