Should you drink electrolytes before running a marathon, competing in HYROX or racing in hot weather? This guide explains sodium preloading, fluid retention, sweat losses and what human studies actually show.
What Is Sodium Preloading Before a Race?
Sodium preloading means consuming sodium and fluid before exercise to help support hydration and fluid retention. It may be useful for selected athletes facing prolonged exercise, substantial sweat losses or hot conditions, especially when drinking during the event will be difficult.
Research shows that sodium-rich drinks can increase fluid retention before exercise. Some studies also report improved endurance in the heat. However, faster running times are not consistently observed, and deliberately drinking excess fluid is not recommended for most athletes.
Based on published human trials and the National Athletic Trainers' Association guidance .
Should You Sodium Preload Before a Race?
Most athletes should focus on arriving at the start adequately hydrated. Special sodium-loading protocols may have a role in selected hot, prolonged events, but they should be individualised and supervised where appropriate. Drinking excessive amounts before a race can create health risks.
The golden rule
Start hydrated, not overloaded.
More sodium and more water do not automatically produce better performance.
What Is Sodium Preloading?
Sodium preloading is a pre-exercise hydration strategy that combines sodium intake with fluid intake.
Sodium is an electrolyte that helps regulate fluid balance, supports nerve signalling and contributes to normal muscle function.
When you sweat, you lose both water and electrolytes, including sodium.
The amount varies considerably between athletes, exercise intensities and environmental conditions.
Normal Hydration vs Sodium Hyperhydration
There are two related but different approaches.
Starting Adequately Hydrated
Drinking and eating normally so you begin exercise with an appropriate fluid balance.
Increasing Fluid Retention
A deliberate protocol intended to retain additional fluid before exercise, sometimes using concentrated sodium solutions.
Important distinction
Research showing that a concentrated sodium drink increases fluid retention does not mean everyone should attempt hyperhydration. Sports medicine guidance generally favours starting exercise normally hydrated.
How Does Sodium Help Your Body Retain Water?
Sodium is the main positively charged electrolyte in the fluid outside your cells.
It contributes to the regulation of fluid distribution and blood volume.
Sodium intake can also influence thirst and the amount of fluid your body retains.
| Entity | Attribute | Role |
|---|---|---|
| Sodium | Electrolyte | Helps regulate extracellular fluid balance |
| Sweat | Fluid loss | Contains water and sodium |
| Plasma volume | Circulating blood component | Contributes to cardiovascular function |
| Thirst | Fluid-intake regulation | Can increase following sodium ingestion |
| Hyperhydration | Pre-exercise strategy | Aims to retain fluid beyond normal hydration |
| Hyponatraemia | Medical condition | Abnormally low blood sodium concentration |
Does sodium increase thirst?
Yes. In a controlled study published in 2015, sodium ingestion increased voluntary water consumption before exercise.
Participants consumed an average of 1,380mL following sodium ingestion, compared with 815mL after placebo.
Fluid retention was also higher: 821mL versus 244mL.
What does this tell us?
Sodium can influence both thirst and fluid retention. But this does not establish that deliberately drinking large quantities is safe or useful for every runner.
Does Sodium Preloading Improve Race Performance?
Several controlled trials show improvements in hydration measures. Performance results depend on the exercise type, conditions and protocol.
Study 1: Eight Endurance-Trained Runners
Eight trained runners consumed a high-sodium or low-sodium beverage before running in 32°C conditions.
The high-sodium drink increased pre-exercise plasma volume by approximately 4.5%.
Among runners who continued to voluntary exhaustion, time to exhaustion averaged:
The researchers also observed reduced physiological strain during exercise in the high-sodium condition.
Research limitation
This was a small laboratory study using a time-to-exhaustion test. The result cannot be translated directly into a percentage improvement in a 10km, marathon or HYROX race.
Study 2: Thirteen Trained Female Cyclists
A study involving 13 trained female cyclists compared high-sodium and low-sodium drinks before exercise in warm conditions.
Time to exhaustion averaged:
The researchers also reported increased plasma volume and reduced thermoregulatory strain with sodium loading.
Study 3: Sodium Before an 18km Run
A different result appeared in a study of six highly trained runners or triathletes.
Participants completed an 18km treadmill time trial in warm conditions, comparing normal hydration with sodium-induced hyperhydration.
Hyperhydration reduced body-mass loss during exercise, but running performance did not improve significantly.
Why the running result matters
An athlete can retain more fluid without running faster. Running also involves carrying body weight, which may change the practical value of additional retained fluid compared with cycling.
Study 4: A Half-Marathon Trial
A more recent study investigated glycerol and sodium chloride in a hyperhydration protocol before a half-marathon in warm conditions.
The protocol improved hydration status, but did not significantly improve half-marathon performance.
Read the half-marathon study .
Sodium vs Salt: What's the Difference?
Sodium and salt are related, but they are not the same measurement.
Table salt is sodium chloride, containing approximately 39.3% sodium by weight.
That means 1,000mg of salt provides approximately 393mg sodium.
| Salt (sodium chloride) | Approximate sodium |
|---|---|
| 500mg | 197mg |
| 1,000mg | 393mg |
| 1,500mg | 590mg |
| 2,000mg | 787mg |
| 3,000mg | 1,180mg |
These are conversion examples, not recommended preloading doses.
Check what the product actually lists
A label stating 1,000mg sodium is different from a label stating 1,000mg salt. Always check the unit and whether the amount refers to sodium or sodium chloride.
How much sodium do you lose in sweat?
Sweat sodium concentration and sweat rate vary considerably between people.
Heat, exercise intensity, acclimatisation, individual physiology and clothing can all affect total fluid and sodium losses.
A useful approach for athletes with substantial sweat losses is to measure sweat rate during training and seek specialist advice where needed.
How to Hydrate Before a Race
For most runners, the starting point is normal hydration rather than aggressive sodium loading.
The following timeline is a practical planning framework, not a fixed sodium or fluid prescription.
Normal Intake
Eat familiar meals and drink normally. Avoid excessive last-minute fluid intake.
Assess Hydration
Consider thirst, usual urine patterns and whether you have been sweating heavily.
Drink Sensibly
Use a familiar fluid routine. Avoid forcing large amounts of water.
Follow Your Plan
Match fluid intake to conditions, duration, thirst and individual needs.
How Much Water Should You Drink Before Running?
There is no single volume that suits every athlete.
Body size, starting hydration, temperature, sweat rate and the time available before exercise all matter.
Sports medicine guidance recommends individualised hydration practices that avoid both dehydration and excessive fluid intake.
Read the NATA fluid replacement position statement .
Should You Take an Electrolyte Drink Before a Race?
An electrolyte drink can provide sodium alongside fluid.
It may be useful in particular circumstances, such as prolonged exercise in hot conditions, but it is not automatically necessary before every race.
The amount of sodium in different products can vary substantially.
Sodium Preloading for Running, Marathons and HYROX
The potential value of sodium preloading depends partly on how long you exercise, how much you sweat and whether you can drink during the event.
| Event | Hydration consideration | Practical priority |
|---|---|---|
| 5km running | Relatively short duration | Start normally hydrated |
| 10km running | Duration and conditions vary | Use a familiar hydration routine |
| Half-marathon | Longer exposure to fluid losses | Plan drinking opportunities |
| Marathon | Prolonged sweat and fluid losses | Individualise fluid and sodium strategy |
| HYROX | Running and functional exercise | Consider race duration, heat and drinking access |
| Ultra-endurance | Extended duration and variable conditions | Develop and test a detailed hydration plan |
Does Sodium Preloading Help HYROX?
HYROX involves eight 1km runs separated by eight functional workout stations.
The combination of running and muscular effort can produce substantial sweating, depending on the athlete and environment.
However, the studies discussed here do not establish that sodium preloading improves HYROX finish times.
The practical focus should be starting adequately hydrated and understanding your expected race duration and fluid needs.
Don't copy a cycling protocol for HYROX
Several positive sodium-loading studies used cycling in hot conditions. Running and HYROX involve different movement patterns and practical demands. The same protocol may not provide the same result.
Can You Drink Too Much Water Before a Race?
Yes. Excessive fluid intake can cause dangerous reductions in blood sodium concentration, known as exercise-associated hyponatraemia.
This risk is particularly important during prolonged exercise when athletes drink more fluid than they lose.
Drinking sports drinks containing sodium does not make unlimited fluid consumption safe.
More fluid is not always better
Overdrinking can be dangerous. Sodium supplements do not reliably prevent hyponatraemia if fluid intake is excessive.
Who Should Avoid Unsupervised Sodium Loading?
Concentrated sodium-loading protocols should not be attempted without appropriate medical guidance by people with conditions such as kidney disease, heart failure or hypertension, or those taking medicines that affect fluid or sodium balance.
Anyone with a history of exercise-associated hyponatraemia should seek individual medical advice before changing their race hydration strategy.
Warning Signs During a Race
Headache, nausea, confusion, unusual weakness or worsening illness during or after prolonged exercise should not be ignored.
Severe confusion, seizures or collapse require urgent medical attention.
Symptoms of dehydration and hyponatraemia can overlap. Do not automatically treat an unwell athlete by encouraging large amounts of water.
Sodium Preloading Research at a Glance
| Study | Participants | Finding | Source |
|---|---|---|---|
| High-sodium drink before running | 8 trained runners | Plasma volume increased by 4.5%; longer time to exhaustion in warm conditions. | PubMed |
| High-sodium drink before cycling | 13 trained women | Time to exhaustion averaged 98.8 vs 78.7 minutes. | PubMed |
| Sodium and voluntary fluid intake | Controlled crossover study | Fluid retained averaged 821mL vs 244mL with placebo. | PubMed |
| 18km running time trial | 6 trained runners/triathletes | Reduced body-mass loss, without significant time-trial improvement. | PubMed |
| Half-marathon hyperhydration | Trained runners | Improved hydration status, without significant performance benefit. | PubMed |
| Female athlete hydration study | 12 cyclists/triathletes | Sodium hyperhydration increased pre-exercise fluid retention by approximately 509mL. | PubMed |
Studies differ in population, temperature, fluid volume, sodium concentration and exercise type. Their results should not be used to predict an individual's race-time improvement.
Sodium Preloading FAQs
What is sodium preloading? +
Should I take electrolytes before running? +
Does sodium preloading improve marathon times? +
Is sodium the same as salt? +
Can I drink too much water before a race? +
Does sodium preloading prevent cramps? +
Should I sodium preload for HYROX? +
How much sodium should I take before a race? +
Start Your Race Hydrated, Not Overloaded
Sodium plays an important role in fluid balance.
Human research shows that sodium-rich drinks can increase pre-exercise fluid retention, and some studies report better endurance performance in hot conditions.
However, better hydration measurements do not always translate into faster running.
For most athletes, the priority is a well-tested hydration routine that suits their race duration, environment and individual fluid needs.
Train Hard. Hydrate Smart. Race Prepared.
Understand your sweat losses, read electrolyte labels carefully and practise your hydration routine during training. Avoid copying aggressive sodium-loading protocols without individual guidance.
Research & Sources
- Sodium loading and fluid balance in trained men exercising in the heat
- Pre-exercise sodium loading in trained female cyclists
- Acute sodium ingestion, thirst and exercise performance
- Sodium hyperhydration and 18km running performance
- Sodium and glycerol hyperhydration before a half-marathon
- Pre-exercise sodium hyperhydration in female athletes
- Systematic review of pre-exercise hyperhydration
- NATA position statement: Fluid replacement for the physically active
- ACSM position stand: Exercise and fluid replacement
- Sodium intake for athletes before, during and after exercise: review and recommendations (2025)
