Fluids for Athletes
Fluids are important for all athletes! Why? Sweat rates vary during exercise from 0.3 to 2.4 L/h dependent on exercise intensity, duration, fitness, heat, acclimatization, altitude, and other environmental conditions (heat, humiditym etc.). Although athletes respond individually to the degree of effects of dehydration, fluid deficits of >2% body weight can compromise cognitive function and reduce aerobic exercise performance, making exercise seem harder. Fluid deficits of 3-5% body weight can affect performance in anaerobic, high intensity sports and aerobic exercise in cool environments. Athletes who are dehydrated are not able to stay as cool during exercise and may develop heat illness.
- To start exercise hydrated and with normal electrolyte levels.
- To avoid decreases in performance due to excessive dehydration.
- To avoid drinking more fluid than needed to replace sweat loss.
- To deliver carbohydrate and electrolytes along with fluid (e.g., sport drink) during prolonged exercise.
- To help maintain core body temperature within acceptable limits.
- To avoid excessive changes in electrolyte balance.
MONITOR YOUR FLUID LOSSES
- Ample, light coloured urine means you are well hydrated.
- Dark, scant urine signals a need for more fluid.
- Weigh yourself before and immediately after exercise – see “Fluids after exercise” below.
Fluids before exercise:
- Drink enough fluid daily to maintain weight and adequate pale yellow colour urine output.
- 5-10 ml/kgBW in 2 to 4 hours before exercise to achieve urine that is pale yellow in colour
- Including sodium in fluids/foods before exercise may help retain the fluid during exercise
Try this in training to find how much fluid is comfortable. LIMIT beverages that contain alcohol.
Fluids during exercise:
Drink enough fluid to prevent excessive dehydration . 6-10% body weight losses and avoid overdrinking. See the conversion exercise below to learn how you can monitor your body weight changes during training and competition to estimate your sweat rate.
- Drink about 0.4–0.8 L of fluid per hour (about 130–250 mL every 20 minutes).
- Test the amount and type of fluid in training.
1 kg weight loss = 1 L of fluid
250 mL = 1 cup = 8 fluid ounces
1 L = 4 cups = 32 fluid ounces
1 kg = 2.2 lbs.
Joanna drank 1 L of water during her two hour practice. She weighed 60 kg before practice and 59 kg after practice. What is Joanna’s sweat rate?
Step 1. Weight loss: 60 kg – 59 kg = 1kg lost
Step 2. Conversion: 1 kg lost = 1 L fluid lost
Step 3. Total fluids: 1 L fluid consumed + 1 L fluid lost = 2 L total sweat loss
Step 4. Sweat rate: 2 L sweat loss ÷ 2 hours = 1 L of sweat per hour of practice
Joanna sweats about 1 L per hour of practice. Next time, Joanna should try to drink close to 1 Litre per hour of practice, in order to limit her weight loss to 1–2 pounds.
Fluids after exercise:
- Replace any fluid and electrolyte deficit. Note that significant dehydration (more than 2–3 pounds weight loss) takes 24–48 hours for complete recovery.
- Athletes who need to exercise again in less than 12 hours should replace fluid loss by 150% (drink 1.5 L of fluid per kg of weight loss). The extra fluid is to compensate for urine lost after drinking a lot of fluid quickly.
- Include sodium with foods or in fluids consumed after exercise. Sodium enhances thirst and fluid retention and helps maintain plasma electrolyte balance.
How much does Joanna (from above) need to drink after practice if she is training again in 6 hours?
Step 1. Weight loss: 60kg – 59kg = 1kg lost
Step 2. C o nversion: 1 kg lost = 1 L fluid lost
Step 3. 150% X loss: 1 L fluid lost X 150% = 1.5 L fluid needed to replace loss
Joanna needs to drink 1.5 L of fluid after practice to recover for her next practice.
AWAY FROM HOME
Although tap water may be “safe” to drink, variations in the bacteria may cause gastro-intestinal upset. Adding ice to drinks is the same as adding tap water.
If you expect to compete in a very hot environment, acclimatize yourself prior to competition by:
- Training in a similar environment prior to departure;
- Traveling to the competition site at least a week prior to competition and gradually increasing your training in those conditions.
If you are not acclimatized and you are exercising in hot, humid conditions, make sure your fluid replacement drink contains sodium. Lightly salt the pre-competition meal or choose foods containing salt (tomato or vegetable juice, salted crackers, soup).
For more information, refer to Exercising in the Heat? If you are training or competing in a hot climate, consult your Canadian Sport Centre physiologist or dietitian for a hydration plan.
FACTORS THAT ENCOURAGE FLUID CONSUMPTION
- Easy access to the beverage
- Chilled drinks (about 0.5 degrees C) will help reduce core temperature when exercising in the heat
- Flavoured beverages
- Sodium added (0.5–0.7 g/L to enhance flavour).
CARBOHYDRATE – ENERGY FOR ENDURANCE:
If exercising more than 1 hour, consume carbohydrate with your fluids.
- Commercial sport drinks containing 6% to 8% carbohydrate (60–80 g/L) are a suitable choice.
Test sport drinks in training, not in competition.
You can make a fluid replacement drink by mixing:
500 mL unsweetened orange juice
500 mL water
1.25–1.75 mL salt
One litre = 54 g (5.4%) carbohydrate and 0.5–0.7 g sodium.
Avoid salt pills! Salt pills are too concentrated, need a lot of water for adequate dilution, and can lead to vomiting and diarrhea.
Recovery after exercise:
- Drink 1.5 L of fluid for every kilogram of weight lost during exercise.
- Consume high carbohydrate foods and drinks.
- Consume foods containing sodium (tomato or vegetable juice, pretzels, commercial soup, low fat cheese, salted nuts) and foods containing potassium (vegetables, fruit, milk, legumes, or meat) to replace electrolytes.