Marathon Aid Station SOP: 4-Stage Intake Rhythm at 5K, 15K, 25K, and 35K

Why Staged Nutrition Matters

A full marathon (42.195K) typically has an aid station every 2.5–5K. If you go all-out at every station, your stomach will slosh; if you skip them all, you’re guaranteed to hit the wall at 30K. The correct approach is “staged, purpose-driven, and proportional.”

Total glycogen stores are roughly 1800–2000 kcal, enough for 75–90 minutes of high-intensity running. A marathoner finishing in 3:30 at race pace burns about 700 kcal per hour, totaling 2450 kcal over the race—450–650 kcal more than what’s stored. That deficit must be filled through nutrition.

Stage 1: Start to 5K (Warm-Up and Stomach Adaptation)

• Aid station action: Water 50–80 ml (half a cup)
• Energy gel: Not needed
• Electrolytes: Not needed
• Purpose: Get the stomach accustomed to eating while running at race pace—this isn’t really about hydration

Key point: Many people skip the first 5K because they’re “not thirsty yet.” But if you don’t drink here, your stomach stays empty and keeps secreting gastric acid, which can lead to acid reflux or stomach cramps at 15K.

Stage 2: 5K to 20K (Establishing the Nutrition Rhythm)

• Every 5K aid station: Water 100–150 ml + sports drink 80 ml
• First energy gel: Take at 45–50 minutes (around 10–12K), with 150 ml of water
• Electrolytes: When the temperature is above 25°C, add one salt tablet at 10K
• Purpose: Establish exogenous carbohydrate flow before glycogen runs out, targeting 30–60g/hr

Research shows the “saturation point” for exogenous carbohydrate intake is 60g/hr (glucose only) or 90g/hr (glucose + fructose mix). Most commercial energy gels contain 22–25g of carbs, so 2 gels per hour plus 200ml of sports drink equals roughly 60g.

Stage 3: 20K to 32K (The Wall-Prevention Zone)

• Every 2.5K aid station: Water 100 ml + sports drink 150 ml
• Energy gel: 1 gel every 30 minutes (around 25K, 28K, 31K)
• Electrolytes: 1 tablet every 8K when the temperature is above 25°C
• Purpose: 30K is the critical point where glycogen runs out; these 12K are the highest-density nutrition segment

Practical tip: Take your last caffeinated gel (80–100mg caffeine) 5 minutes before 30K to delay central fatigue.

Stage 4: 32K to the Finish (Sprint-Maintenance Zone)

• Aid stations: Water 80 ml at every station, sports drink 150 ml
• Energy gel: Take 1 gel at 35K (the final one)—caffeinated is better
• Electrolytes: Depends on your personal cramping history; most people don’t need them at this point
• Purpose: Maintain blood sugar and avoid dehydration, but avoid overloading the stomach

At this stage, gastrointestinal blood flow has dropped significantly to about 25% (vs. 100% at rest), so gastric emptying slows down. Eating too much means it won’t digest—and you’ll get stomach cramps. When in doubt, do less.

What to Carry

For finishers targeting 3:30–4:00, carry 5 energy gels (don’t rely on race-provided ones, in case they run out):

• Gel 1: 12K
• Gel 2: 20K
• Gel 3: 26K (caffeinated)
• Gel 4: 30K
• Gel 5: 36K (caffeinated)

Clip 3 salt tablets on your body, taking them at 10K, 20K, and 30K (when the temperature is above 25°C).

Mandatory Rehearsal 14 Days Before the Race

Your nutrition strategy must be fully rehearsed once during a long run (32K simulation) 14 days before race day. This includes:

• The same energy gel (brand, flavor, caffeine content)
• The same electrolytes
• The same intake rhythm
• The same carrying method (belt pack vs. shorts pockets)

Never try anything on race day that you haven’t practiced. The gut is the most sensitive organ during a race—something new could be the start of a DNF (Did Not Finish).

Conclusion

Marathon nutrition isn’t about “drinking when thirsty”—it’s an engineering plan arranged in advance according to the glycogen depletion curve. Write the four stages’ intake amounts on a wrist sticker, follow the plan at every aid station, and your odds of hitting the wall at 30K will drop dramatically.

Related Reading

• Marathon Aid Station Food Choices: How to Refuel Without Stopping
• Marathon Course Aid Station Strategy: The Art of Distributing Water, Sports Drinks, and Energy Gels
• Marathon Aid Station Strategy: When to Drink Water and When to Take Energy Gels
• Road Race Aid Station Food Selection Strategy: Making Energy Gels Not Your Only Option