Hydration & Electrolytes for Endurance Athletes: What You're Missing

You can train perfectly, fuel correctly, and still fall apart on race day — all because of hydration.

Most endurance athletes focus on carbs, but hydration and electrolytes are the foundation that keeps your engine running. Get them wrong, and no amount of gels will save you.

Let's break down the real science of hydration for endurance athletes, how electrolytes work, and how to avoid the mistakes that wreck performance.

Even a 2% drop in body weight from fluid loss can decrease performance, increase heart rate, and raise your perceived effort. By 4–5%, you're flirting with dizziness, cramps, and heat exhaustion.

Hydration isn't just about drinking more — it's about balancing water with electrolytes, especially sodium.

Electrolytes are minerals that conduct electrical signals in your body. They control nerve function, muscle contraction, and fluid balance.

Sodium is the MVP here. It helps your body retain fluid and transport glucose into muscles during long efforts. If you drink only water, you dilute your sodium levels — leading to hyponatremia, a dangerous condition that can cause confusion, nausea, or worse.

Hydration isn't one-size-fits-all. Your needs depend on body size, weather, and sweat rate.

• Fluid: 400–800 ml/hour (13–27 oz)
• Sodium: 400–800 mg/hour
• Potassium: 100–200 mg/hour
• Magnesium: 10–20 mg/hour

A simple rule: If your body weight drops more than 2% after training, you're underhydrating. Weigh yourself before and after long workouts to get your personal sweat rate.

• Thirst or dry mouth
• Dark yellow urine
• Dizziness or nausea
• Rapid heart rate during easy effort
• Muscle cramps
• Headache after long runs or rides

If two or more of these show up — it's time to fix your hydration plan.

You don't need to guzzle water all morning. Instead, sip steadily and include electrolytes.

• Drink 500–700 ml (17–24 oz) of fluid
• Include 300–500 mg sodium
• Add carbs if the workout will exceed 90 minutes

Pro tip: Avoid starting overhydrated — clear urine before a race is not the goal. Pale yellow means perfect balance.

Your aim during training is to replace what you lose, not to overcompensate.

If you train in hot or humid conditions, you may need 20–30% more.

After training, replace 150% of the fluid you lost within a few hours. If you lost 1 lb (0.45 kg), drink about 700 ml (24 oz) to restore balance.

Pair this with electrolytes + carbs to enhance glycogen replenishment. Skip the plain water — your kidneys will just flush it out.

• Carbs: 1–1.2 g/kg
• Protein: 20–30 g
• Sodium: 500–800 mg

• ❌ Relying on thirst. By the time you feel thirsty, you're already 2% dehydrated.
• ❌ Drinking only water. This dilutes sodium and risks cramps or hyponatremia.
• ❌ Not testing sweat rate. Your hydration needs are personal — guessing rarely works.
• ❌ Ignoring heat and humidity. Hotter conditions increase fluid and sodium loss dramatically.
• ❌ Skipping carbs in fluids. Carbs + sodium = better absorption and steady energy.

MAVR brings hydration science into your training automatically.

• Uses your training calendar to identify long or hot sessions
• Adjusts your hydration and sodium targets for each day
• Suggests pre-, during-, and post-workout hydration goals
• Combines fueling + hydration advice in one adaptive plan

No spreadsheets. No guessing. Just AI-powered guidance that ensures you're fueling and hydrating right.