Maintaining electrolyte balance during a 100-mile race requires orchestrating sodium, potassium, magnesium, and calcium intake across 16-30 hours while your body is in metabolic chaos. Get it wrong and you’re shuffling at mile 60 with cramping legs or slumped in a medical tent with hyponatremia. This complete guide to electrolyte balance for 100-mile races provides the precise timing and dosing that separates finishers from DNFs.
The Four Critical Electrolytes
Sodium: The Primary Player
Function: Fluid balance, nerve signaling, nutrient absorption Losses: 500-2,000mg per hour through sweat Target intake: 500-1,000mg per hour early race, 300-600mg hours 16+
Sodium dominates electrolyte balance because it’s lost in highest quantities and most directly impacts performance. Focus 70-80% of your electrolyte strategy on sodium replacement.
Potassium: The Muscle Stabilizer
Function: Muscle contraction, heart rhythm, cellular fluid balance Losses: 100-300mg per hour Target intake: 150-300mg per hour (mostly through food)
Unlike sodium which concentrates in sweat, potassium primarily stays in blood. Most runners meet potassium needs through bananas (422mg each), potatoes (610mg per medium), and sports drinks without dedicated supplementation.
Magnesium: The Cramping Preventor
Function: Muscle relaxation, energy production, nerve function Losses: 10-50mg per hour Target intake: 50-100mg every 2-3 hours
Magnesium deficiency contributes to cramping more than sodium deficiency in many runners. Small, frequent doses work better than large boluses which cause diarrhea.
Calcium: The Often-Forgotten Mineral
Function: Muscle contraction, bone health, nerve transmission Losses: 20-80mg per hour Target intake: 100-200mg every 3-4 hours
Least discussed but still important for muscle function. Usually adequate through dairy-based recovery drinks and certain electrolyte products.
Phase-Specific Electrolyte Balance Strategy
Phase 1: Hours 1-8 (Miles 0-50)
Sodium: 600-1,000mg per hour Potassium: 150-200mg per hour Magnesium: 50mg every 2 hours Calcium: 100mg every 4 hours
Delivery method: – Sports drinks: Base sodium and potassium – Salt tablets: 1-2 per hour – Salty solid foods: Pretzels, chips, salted potatoes – Magnesium capsule: Every other hour
Early race electrolyte balance prevents deficits from accumulating. Front-loading sodium while absorption is optimal provides buffer for late-race challenges.
Phase 2: Hours 9-16 (Miles 50-75)
Sodium: 500-800mg per hour Potassium: 150-200mg per hour Magnesium: 75mg every 2 hours Calcium: 150mg every 3 hours
Delivery method: – Continue sports drinks – Reduce salt tablets: 1 per hour – Increase food-based electrolytes: Broth, pickles – Magnesium: Increase slightly as cramping risk peaks
Mid-race is where electrolyte balance becomes challenging. Stomach distress may limit supplementation—prioritize sodium, accept modest potassium/magnesium deficits if necessary.
Phase 3: Hours 17-24+ (Miles 75-100)
Sodium: 300-600mg per hour Potassium: 100-150mg per hour Magnesium: 50mg every 2-3 hours Calcium: 100mg every 4 hours
Delivery method: – Simple sports drinks or broth – Minimal salt tablets (stomach often can’t tolerate) – Food-focused: Whatever stays down – Consider IV saline if medical team available and severe depletion
Late-race electrolyte balance shifts to “whatever works.” If you’ve front-loaded early, conservative late intake suffices.
Electrolyte-Rich Foods for 100-Mile Aid Stations
High Sodium Options
Chicken broth: 700-900mg sodium per cup + warm comfort Ramen noodles: 800-1,200mg per serving Pickles: 300-400mg per large pickle Salted boiled potatoes: 200-400mg (add liberal salt)
Potassium Sources
Bananas: 422mg potassium Baked potato (with skin): 610mg potassium Orange juice: 496mg per cup Dates: 167mg per 3-4 dates
Magnesium Sources
Almonds: 80mg per ounce (hard to digest while running) Spinach: 157mg per cup (rarely at aid stations) Magnesium supplements: Most reliable for racing
Warning Signs of Electrolyte Imbalance
Sodium Deficiency (Hyponatremia)
- Nausea and vomiting
- Headache
- Confusion or altered mental state
- Swollen hands/fingers
- Muscle weakness
Potassium Deficiency
- Muscle weakness and fatigue
- Cramping (along with magnesium)
- Irregular heartbeat
- Extreme thirst
Magnesium Deficiency
- Muscle cramping and twitching
- Numbness or tingling
- Abnormal heart rhythms
- Personality changes
Supplementation Products
Multi-Electrolyte Tablets
SaltStick Caps: 215mg sodium, 63mg potassium, 11mg magnesium, 22mg calcium Target dosage: 1-2 caps per hour early race
LMNT packets: 1,000mg sodium, 200mg potassium, 60mg magnesium Target dosage: 1 packet every 2-3 hours
Standalone Supplements
Salt tablets (sodium chloride): 200-400mg per tablet Magnesium glycinate: 100-200mg per capsule (best absorption) Potassium supplements: Generally unnecessary—get from food
Key Takeaways
- Electrolyte balance for 100-mile races requires 500-1,000mg sodium per hour early, decreasing late race
- Potassium (150-300mg/hour) comes primarily from food: bananas, potatoes, sports drinks
- Magnesium (50-100mg every 2-3 hours) prevents cramping more effectively than excess sodium
- Front-load electrolytes hours 1-8 when absorption is optimal
- Late race (hours 17+) use whatever stays down: broth, simple drinks, minimal supplements
- Monitor swollen hands and confusion as warning signs of sodium imbalance
Execute Your Electrolyte Strategy
Electrolyte balance in a 100-mile race isn’t about perfect precision—it’s about preventing catastrophic deficits while adapting to changing GI tolerance. Start aggressively with 600-1,000mg sodium hourly, maintain mid-race, and accept reduced intake late when stomach rebels.
Test your complete electrolyte protocol during back-to-back long weekend runs that simulate ultra fatigue. Practice timing supplements around aid stations, mixing products for variety, and adjusting when nausea hits. Your race-day electrolyte balance should be muscle memory, not mental math at mile 75.
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