Hydration for Athletes
(and Coaches)
Dr John Bradley
Hydration for Athletes
(and Coaches)
You need 8 glasses of water a day
It is easy to become dehydrated
You lose lots of salt in sweat
Sweating is a sign of lack of fitness
Dr John Bradley
If you do sport you need a
sports drink
Drink - Why?
Male
(80kg)
Female
(65kg)
Water
60%
(48 litres)
52%
(34 litres)
Turnover
(litres)
2.4 - 4.8
1.7 - 3.4
Fluid &
Activity
1.31
ml/kcal
1.20
ml/kcal
2%
1.6 kg
1.3 kg
Dr John Bradley
How Much?
Age
(yr)
Male
(l/d)
Female
(l/d)
1-3
1.3
1.3
4-8
1.7
1.7
9-13
2.4
2.1
14-18
3.3
2.3
>19
3.7
2.7
Dietary Reference Intakes:
Food & Nutrition Information Centre (FNIC),
US Department of Agriculture
• 6-8 glasses of
water/day (≈ 2 litre)
– Stare & McWilliams
(1974)
• 1.25 litres adequate
– Valtin et al (2002)
• Food is a good
source of water.
– ≈ 1 litre/day
Dr John Bradley
Am I hydrated?
Dr John Bradley
Sweating is Good!
Dehydration Impairs Sweating
Bradley & Gardner (2002).
Dr John Bradley
Sweating
Hockey
Tournament;
Madrid, June.
29ºC, 50% RH
Weight Loss
(kg)
Average
0.38
Maximum
2.4
Minimum
-1.4*
* Substitute
Average Player mass = 73 kg
(2% = 1.5kg)
• Sweat:
– Water
– Electrolytes
• Replace
– Water
– Electrolytes
Dr John Bradley
What to Drink
Fluid
Sodium (mmol/l)
Water
0
Soft Drink
1-3
Sports Drink
10-25
Oral Rehydration Solution
50-60
5.8g NaCl (1 tsp) per litre
100
Maughan & Leiper (1995)
Dr John Bradley
Isotonic Energy Drink
• Water
• Sodium
– 25mmol ≈ 0.25 teaspoon salt in 1 litre
• Carbohydrate
–
–
–
–
8% ≈ 80g per litre
Lucozade Sport = 6.4%
Lucozade Sport Lite = 2%
Coca-Cola = 10.6%
• Best drink
– Tastes the best!
Dr John Bradley
Hydration Strategies
• Insist on own, named
water bottles at
practice
• Hold them during
– Team talks
– Warm-up
– Warm-down
• Recovery starts at the
final whistle
• Observe body
• Drink ~0.5 litre
electrolyte drink two
hours before activity
• Drink regularly during
activity if possible.
• Get into the Habit
Dr John Bradley
Hydration for Athletes
(and Coaches)
It is easy to become dehydrated
Fact:
Dehydration is usually defined as
losing 2% body weight, or losing
1.7kg for a 70kg person.
You need 8 glasses of water a day
Fact:
Drink according to your needs
You lose lots of salt in sweat
Fact:
Sweat is very dilute in salt.
Sweating is a sign of lack of fitness
Fact:
Sweat rates are quite individual. The higher
the exercise intensity, the more heat
generated, the higher the sweat rate.
Sweating is a sign of a well prepared athlete.
Dr John Bradley
If you do sport you need a
sports drink
Fact:
Water, milk, diluted juice are
good beverages for activities
under 60min. Energy drinks are
useful for events lasting 60min or
more.
References
•
Bradley, J. & Gardner, L. (2002). Assessment of the relationship
between pre-hydration and weight loss during exercise. Medicine &
Science in Sports & Exercise. 34(5), S148
•
Food & Nutrition Research Centre, US Department of Agriculture:
http://fnic.nal.usda.gov/
•
Maughan, R.J. & Leiper, J.P. (1995). Sodium intake and postexercise rehydration in man. Eur. J. Appl. Physiol. 71(4), 311-319.
•
Stare, F.J. & McWilliams, M. (1974). Nutrition for good health.
Plycon Press, p. 175.
•
Wilmore, J.H., Costill, D.L. & Kenney, W.L. (2008). Physiology of
Sport and Exercise, Human Kinetics.
•
Valtin, H. (2002). “Drink at least eight glases of water a day.” Really?
Is there scientific evidence for “8 x 8”? Am. J. Physiol. 283, R993R1004.
Dr John Bradley
Questions?
Dr John Bradley