Marathon Aid-Station Hydration: Build a Course Card

The short answer

Build a marathon hydration plan from the current official aid-station map, products you have already tolerated, expected conditions, and your own training observations. Write a station-by-station card with three branches: normal conditions, hotter-than-practised conditions, and a stop-or-seek-help rule.

Do not turn a sweat-rate estimate into an instruction to replace every millilitre lost. Hydration guidance emphasizes individualized plans and warns against both substantial dehydration and excessive drinking.1

Collect the course facts first

Use the organizer's current athlete guide or event page. Record:

• exact or approximate station locations;
• water and sports-drink availability;
• which product and concentration are supplied;
• cup, bottle, refill, or self-carry rules;
• gel or food locations;
• weather and course alerts;
• any event-specific medical guidance.

If the organizer has not confirmed a product, mark it unknown. Do not assume the brand from last year's race or a sponsor logo. If station spacing is approximate, build tolerance into the plan rather than writing false precision.

Separate four numbers

Runners often combine different quantities into one target:

1. Sweat rate estimate: a training observation influenced by conditions, effort, clothing, and measurement error.
2. Planned fluid intake: what you intend to drink across time or stations.
3. Carbohydrate intake: fuel that may come from gels, drinks, or food.
4. Sodium intake: from drinks, gels, food, capsules, and ordinary diet.

They interact, but they are not interchangeable. A sports drink can contribute fluid, carbohydrate, and sodium. Water may be needed with a concentrated gel. Adding products without counting the total can create gastrointestinal or overdrinking problems.

The marathon sweat-rate worksheet can organize a before-and-after training estimate. Use the marathon carbohydrate guide to keep fueling compatible with drinking.

Make the station card

Replace the generic rows with actual official stations. The card should fit on one screen or small sheet.

Use a sweat test as a range, not a verdict

A field estimate usually compares body mass before and after a representative session, accounting for fluid consumed and urine produced.3 Repeat it in different relevant conditions. One cool easy run cannot predict a hot marathon.

Measurement has limits:

• home scales vary;
• clothing may hold water;
• body mass changes for reasons besides sweat;
• intensity and acclimatization alter the result;
• the marathon may last much longer than the test.

Use the result to identify whether your current intake is mismatched and to frame a practised range. Do not assume that replacing 100% of measured loss is required or safe.

Avoid the two dangerous simplifications

“Never drink until thirsty”

Some athletes, conditions, and event durations benefit from a more structured individualized plan. Thirst is useful information, but it is not the only input.1

“Drink at every station”

Station frequency is a logistical choice by the organizer, not a prescription for every runner. Drinking beyond need can contribute to exercise-associated hyponatraemia, especially when fluid intake exceeds losses.2

The safe middle is a tested plan with awareness of thirst, conditions, pace, symptoms, and total intake.

Build three branches

Normal conditions

Use the intake range rehearsed in long runs at similar effort and conditions. Specify which stations are planned and what product is used.

Hotter or more humid than practised

Do not respond only by drinking more. Lower early effort, use available cooling, adjust expectations, and follow event guidance. Heat acclimation and heat-illness prevention involve pacing, preparation, and risk recognition as well as fluid.4

Your branch might say: “Start slower, use official cooling, reassess at each planned station, and do not exceed the tested intake range without a clear reason.” Individual needs vary; qualified sports dietetic or medical guidance is appropriate for high-risk cases.

Stop or seek help

Confusion, collapse, fainting, severe breathing difficulty, chest pain, loss of coordination, or worsening heat-illness symptoms are not cues to force more fluid and continue. Seek event medical help. Hyponatraemia and heat illness can share nonspecific symptoms, so self-diagnosing the problem mid-race is unsafe.2

Make fueling compatible

Write the carbohydrate source beside each planned drink:

• gel plus water;
• measured sports drink;
• organizer-provided product already tested;
• personal bottle or soft flask permitted by the event.

Distance-running nutrition guidance supports individualized, practised carbohydrate strategies.6 It does not make a new race-expo sample safe. If the on-course product differs from training, carry a permitted familiar alternative or create a conservative backup.

Also count caffeine across gels, drinks, and tablets. Race day is not the time to discover how several sources combine.

Practise the mechanics

A hydration plan can fail because the athlete cannot execute it. During selected long runs, practise:

1. seeing the station and choosing a line early;
2. slowing enough to take the cup safely;
3. drinking without gasping;
4. discarding the cup only in the permitted zone;
5. rebuilding running rhythm without sprinting;
6. remembering whether fuel was actually consumed.

Rehearse with the same carrying system and concentration. If a vest, belt, handheld bottle, or soft flask changes posture or causes rubbing, resolve that before race week.

A worked card

Suppose an organizer provides water every 5 km and sports drink at 10, 20, 30, and 35 km. A runner has practised water with gels and small servings of that exact sports drink.

Their card might say:

• 5 km: optional water within tested range; settle effort.
• 10 km: planned sports drink; count its carbohydrate.
• 15 km: water with familiar gel.
• 20 km: sports drink only if stomach and effort are stable.
• 25 km: water with familiar gel.
• 30 km: reassess conditions and symptoms; use planned product.
• 35 km: water or sports drink according to tested branch, not both automatically.
• 40 km: drink only if needed and safely manageable.

Those stations and choices are illustrative, not recommended quantities. Each actual race and runner requires its own card.

Final 48-hour check

Confirm the latest organizer guide, forecast, station products, and carrying rules. Do not try to “pre-hydrate” by forcing excessive fluid. Maintain familiar meals and drinking habits unless a qualified clinician or sports dietitian has given an individual protocol.

26weeks.ai keeps the race date, long runs, and missed sessions together so race-week decisions can stay connected to the training that actually happened. Start training now.

This guide is educational and not medical advice. Athletes with kidney, heart, endocrine, or fluid-balance conditions, or a history of heat illness or hyponatraemia, should obtain individualized clinical guidance.

References

1. American College of Sports Medicine. Exercise and fluid replacement position stand. (PubMed)
2. Third International Exercise-Associated Hyponatraemia Consensus. (PubMed)
3. Gatorade Sports Science Institute. Sweat testing methodology in the field. (Method)
4. Racinais S, et al. Exercise-heat acclimation and heat-illness prevention. (PubMed)
5. American College of Sports Medicine. Exertional heat illness position stand. (PubMed)
6. Burke LM, et al. Contemporary nutrition strategies for distance runners. (PubMed)
7. World Athletics. Nutrition for Athletics consensus materials. (Official library)
8. Ramos-Campo DJ, et al. Acute carbohydrate feeding and endurance performance: systematic review and meta-analysis. (PubMed)