Training Guides / Nutrition basics
Hydration for training
How much water you need, how to tell if you are drinking enough, and when sports drinks and electrolytes actually help during and after exercise.
Water makes up roughly half to 60 percent of an adult's body weight. It regulates temperature through sweat, carries nutrients, cushions joints and keeps blood volume up so your heart can pump efficiently. Losing even a small percentage of body weight as sweat can make exercise feel harder, especially in the heat.
General education only. People with heart, kidney or other medical conditions, or those on fluid restrictions, should follow their doctor's advice.
How much water per day?
The US National Academies of Sciences, Engineering, and Medicine set adequate intakes for total water (from all drinks and food) of about:
| Group | Total water per day |
|---|---|
| Adult men | About 3.7 liters (about 125 fl oz) |
| Adult women | About 2.7 liters (about 91 fl oz) |
Roughly 20 percent of that usually comes from food, so drinks make up the rest. Needs rise with heat, humidity, body size and exercise. These figures are averages, not strict targets.
Simple ways to check
- Urine color: pale yellow usually means you are well hydrated. Dark yellow suggests you need more. Some vitamins can make urine bright yellow regardless.
- Thirst: for most healthy people during everyday life, drinking when thirsty works well.
- Body weight before and after training: each kilogram lost during a session is roughly a liter of sweat not replaced.
Before, during and after exercise
| When | Practical guidance |
|---|---|
| Before | Start well hydrated. Drink with your meal a few hours before and a glass of water in the hour before |
| During | For typical lifting sessions, sip water as you like. For long or hot sessions, drink regularly to limit sweat losses |
| After | Rehydrate with water and a meal. If you lost a lot of sweat, drink a little more than the weight you lost over the next few hours |
Electrolytes and sports drinks
Sweat contains water and electrolytes, mostly sodium, with smaller amounts of potassium. For most gym sessions under about an hour, water plus normal meals replace everything you need.
Sports drinks or electrolyte mixes can help when:
- Sessions last longer than about 60 to 90 minutes
- You train hard in heat or humidity
- You are a heavy or "salty" sweater (white salt marks on clothes)
- You train twice in one day
Overhydration
Drinking far more water than you lose, especially during long endurance events, can dilute blood sodium to dangerous levels, a condition called hyponatremia. It is rare in gym training but has occurred in marathon runners and hikers. Drink to thirst and match losses rather than forcing large volumes.
Symptoms of heat illness include dizziness, nausea, headache, confusion and stopping sweating in hot conditions. Stop exercising, move somewhere cool and get medical help if symptoms are severe or do not improve.
Caffeine and alcohol
Moderate caffeine intake from coffee or tea contributes to daily fluid needs for regular users. Alcohol increases fluid loss and can impair recovery and sleep, so keep it moderate, especially after hard training. See sleep and recovery and supplements for more on caffeine.
Keep a water bottle with you through the day and refill it a set number of times. It is easier than counting glasses.
