Hydration for Runners: Sweat Rate, Sodium, and Pre/During/Post Run Strategy
“Drink as much as possible” conflicts with bloating and hyponatremia risk; “drink only when thirsty” conflicts with long hot races where thirst lags. The workable middle is personal sweat rate plus a simple plan. Energy context: Calories Calculator; heat pacing in the hot weather guide; carbs on the move in long-run fueling. Easy days still need Zone 2 honesty via the Zone 2 Calculator.
Sweat Rate Beats Generic Rules
Weigh yourself nude before and after a 60-minute easy run (no bathroom stops if possible). Fluid ounces/ml lost ≈ sweat loss after adding any fluid drunk. Divide by hours for a starting hourly target — then adjust for hotter/cooler days.
Numeric scenario: Pre-run 70.0 kg, post-run 69.3 kg after drinking 300 ml in 60 minutes → loss = 0.7 kg + 0.3 kg = 1.0 L/hour sweat. A starting plan might replace ~600–800 ml/hour mid-run (not necessarily 100% of sweat) plus sodium in the bottle or tabs. If you finish with white salt crust and pounding headache on hot days, raise sodium into a few-hundred-mg-per-hour range that your gut tolerates — individual needs vary widely.
Overdrinking plain water on long events can dilute sodium. Practice race bottles on long runs. Watch “hydration reminders” are guesses — your sweat test beats a generic buzz.
Decision rule: if body weight is down >2–3% after a key long run with poor feel, increase mid-run fluid next time. If you slosh, nausea, or gain weight during a run, drink less per hour and slow your sip rate.
Pre / During / Post
- Pre: start euhydrated; pale straw urine is a rough cue
- During: small sips on a schedule you’ve practiced
- Post: meals + fluids; include salty foods after heavy sweat
Retest sweat rate in a new season — summer and winter numbers differ. Keep caffeine and alcohol in mind the day before long efforts; both can shift fluid status. Practice the exact bottle, mix, and schedule you plan to use in the race, including the awkward “open packet while jogging” skill.
Practical Takeaway
Measure, practice, and match bottles to weather — not to internet absolutes. Gut comfort is part of the prescription.
FAQ
Do I need sports drink for every easy run?
Usually no for <60 minutes in mild weather. Longer/hotter sessions benefit more from planned fluid and sometimes carbs/sodium.