Athlete Rehydration: What to Drink Before, During, and After Training

Staying properly hydrated is one of the most reliable ways to improve performance, reduce injury risk, and recover faster. This guide shows exactly how much to drink, what to include (electrolytes and carbs), and how to personalize your plan using sweat rate and body-weight changes.

Why rehydration matters

• Performance starts dropping at ~2% body mass loss from dehydration.
• Dehydration raises heart rate and perceived exertion, and can impair decision making.
• Proper sodium intake helps retain fluid and prevents cramping for many athletes.

Quick-start summary

• Pre: 5–10 mL/kg of fluid 2–4 hours before training. Top-up 5–10 minutes before if urine is dark.
• During: 0.4–0.8 L/hour for most athletes; adjust to conditions and body size.
• Sodium: 300–600 mg/hour in hot/humid conditions or for “salty sweaters.”
• Carbs: 30–60 g/hour for sessions >60–90 minutes (up to 90 g/h for ultra).
• Post: 1.25–1.5 L per kg of body mass lost, plus sodium, within 2–4 hours.

Rule of thumb: 1 kg (2.2 lb) of weight lost ≈ ~1 L of sweat/fluid deficit.

Before training (Pre-hydration)

• 2–4 hours pre: 5–10 mL/kg (e.g., 350–700 mL for a 70 kg athlete).
• If urine is dark 30 minutes pre, add 200–300 mL.
• Include a pinch of sodium (or an electrolyte tab) if you tend to sweat heavily or train in heat.

What to drink

• Water for short, easy sessions.
• Water + electrolytes for intense or hot sessions.
• Optional: light carbs (15–30 g) if starting glycogen is low.

During training

How much

• Start with 0.4–0.8 L/hour; fine-tune using your sweat rate (see below).
• Small, frequent sips every 10–15 minutes usually feel best.

What to include

• Sodium: 300–600 mg/hour in heat/humidity; less may be fine in cool conditions.
• Carbs:
  • 30–60 g/hour for 60–150 min sessions.
  • Up to 90 g/hour (glucose+fructose mix) for >2.5 hours.

Signs to adjust

• Cramps, dizziness, pounding heart: more fluids and sodium.
• Sloshing stomach or GI distress: slow down intake; reduce concentration or total volume.

After training (Rehydration)

• Weigh before and after sessions. Each 1 kg lost → drink 1.25–1.5 L over the next 2–4 hours.
• Include sodium to improve fluid retention (e.g., 500–1000 mg spread over rehydration).
• Combine fluids with a balanced recovery meal (protein + carbs).

Calculate your sweat rate (simple method)

1. Weigh nude pre- and post-workout.
2. Track all fluids consumed (L) and urine (if any).
3. Sweat loss (L) ≈ (Pre kg − Post kg) + Fluids consumed − Urine.
4. Sweat rate (L/h) = Sweat loss ÷ Duration (hours).

Use this to set your during-training target: aim to keep weight loss under ~2%.

Example plans

60-minute interval run (cool weather)

• Pre: 500 mL water 2 hours before.
• During: 300–400 mL water; add 300 mg sodium if you tend to cramp.
• Post: If 0.5 kg down → 0.7 L across the next 2 hours with a salty snack.

90-minute ride (moderate heat)

• Pre: 600 mL water + electrolyte tab 2–3 hours before.
• During (target ~0.6 L/h): 900 mL total with ~600 mg sodium and 45 g carbs.
• Post: If 1.0 kg down → 1.3–1.5 L plus 800–1000 mg sodium over 2–3 hours.

2-hour team sport practice (hot/humid)

• Pre: 700 mL electrolyte drink 2–3 hours before.
• During (target ~0.8 L/h): 1.6 L total with 600 mg sodium/h and 60 g carbs/h.
• Post: If 1.5 kg down → ~2.0 L across 2–4 hours with a salty meal.

Avoid overhydration (hyponatremia)

• Don’t force excessive plain water beyond thirst in long events.
• Include sodium during prolonged sweating and in the rehydration window.
• Use body weight checks to guide, not exceed, your needs.

Practical checklist

• Weigh in/out on key training days.
• Log fluid, sodium, carbs, and conditions (heat/humidity).
• Set targets: pre (mL), during (L/h + mg sodium + g carbs), post (L + sodium).
• Review weekly and adjust.

FAQ

How do I know I’m hydrated before training?
Pale-yellow urine, minimal thirst, and stable morning weight are good signs.

Do I need sports drinks for short sessions?
Usually no, water is fine for <60 minutes unless it’s hot or very intense.

What if I get stomach issues with sports drinks?
Try lower concentration (e.g., 3–4% carbs), smaller sips, or different carb sources (glucose+fructose).

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Further reading

• Hydration for athletes
• Electrolytes 101
• Daily water intake guide