The Complete Electrolyte Guide for Ultra Runners

Electrolyte supplementation is one of the most confusing topics in ultra running. Every brand claims their formula is the best. Here's what the research actually says.

What Are Electrolytes?

Electrolytes are minerals that carry an electrical charge in your body. The key ones for runners are sodium, potassium, magnesium, and calcium. You lose them through sweat, and if you don't replace them, bad things happen — cramping, nausea, confusion, and in extreme cases, hyponatremia.

How Much Sodium Do You Need?

The average runner loses 800–1,200mg of sodium per hour through sweat. Heavy sweaters can lose up to 2,000mg/hour.

General guideline: Replace 500–700mg of sodium per hour during ultras. If you're a heavy sweater or it's a hot day, go up to 1,000mg.

The Best Electrolyte Products

For simplicity: Tailwind Endurance Fuel provides ~300mg sodium per serving plus calories. Use as your primary fuel source.

For heavy sweaters: LMNT provides 1,000mg sodium per packet with zero sugar. Mix in water between aid stations.

For prevention: SaltStick caps provide 215mg sodium per capsule. Take 1–2 per hour on hot days in addition to your normal fuel.

The Research

A 2024 study in the Journal of the International Society of Sports Nutrition found that sodium supplementation during ultras longer than 50K reduced finish times by an average of 26 minutes compared to water alone. The effect was most pronounced in hot conditions and in runners who described themselves as heavy sweaters.

Warning Signs of Electrolyte Imbalance

• Muscle cramps that don't resolve with stretching
• Nausea or bloating in the second half of a race
• Confusion or difficulty making decisions
• Puffy fingers or hands (possible hyponatremia)

If you experience confusion or significant swelling, seek medical help immediately.

The Bottom Line

Start with 500mg sodium per hour. Adjust up in heat or if you're a heavy sweater. Practice in training so you know what works for you.