SPORT SCIENCE & MEDICINE TEAM
FLUID GUIDELINES
INTRODUCTION
These guidelines are to ensure effective hydration strategies are employed by athletes and staff both
during training and competition.
Fluid loss during exercise is linked to the need to maintain body temperature within narrow limits and
unless fluid intake keeps pace with sweat loss, dehydration can result, leading to adverse
cardiovascular and themoregulatory consequences and then fatigue and poor performance.
THE EFFECTS OF DEHYDRATION
o
Exercise performance can be impaired by 10-20% if dehydrated by as little as 2% of body
weight
o
Fluid losses in excess of 3% increases the risk of heat cramps, heat exhaustion or heat stroke
o
Dehydration can affect mental function, slowing reaction-response times and decision making
skills, which are vital in team sports.
Fluid loss depends on sweat rates and can vary between 500-2000ml per hour depending on
environmental temperature. Fluid should be replaced during exercise preferably at a rate equal to
sweat rate. It is important not to over consume fluids as this may potentially cause the problem of
hyponatremia.
SWEAT RATE
All athletes should know their sweat rate and aim to consume sufficient fluid during each training
session/game to match fluid losses.
To calculate sweat rate:
o
Record pre training weight (kg) in minimum clothing
o
Record post training weight (kg) removing sweaty clothing first
o
Subtract post training weight from pre training weight to obtain weight lost – convert kg to
g’s i.e. multiply by 1000. For example if weight loss is 1.2kg this would be 1200g
o
Record the amount of fluid (ml) consumed during training i.e. weigh drinks bottles before
and after training, noting any refills
o
Record volume of any urine (ml) passed during that time (this volume will only be subtracted
if urine was passed prior to post exercise body weight)
o
Record the length of time spent training in hours
SWEAT RATE = (Pre exercise body weight – post exercise body weight) + fluid intake –
urine volume, Exercise time in hours
o
1 kg weight loss equates to 1 litre fluid loss
o
For every kg of weight lost, 1.25 -1.5litres fluid is needed to replace it due to the continuing
loss of sweat after exercise finishes and the urine losses that persist even in the dehydrated
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state. This will ensure optimal hydration is achieved after the event.
Sample sweat rate calculation
A
Name
Athlete A
B
Date
12-Mar
C
Body Weight before exercise
61.7Kg
D
Body weight after exercise
60.3Kg
E
Change in BW (C-D)
1.4kg 1400g (Kg x1000)
F
Drink volume
420ml
G
Urine volume
90ml
H
Sweat loss
1730ml (E+F-G)
I
Exercise time
90min (1.5hrs)
J
Sweat rate (H/L)
19ml/min, 1153ml/hr
Athlete A should therefore consume just over 1 litre per hour to keep up with sweat rate and
maintain a good hydration status
TIMING OF FLUID INTAKE
During exercise, fluids should be replaced at a rate equal to sweat rate, which will vary depending on
exercise intensity, temperature, humidity, hydration status, acclimatisation and the type of clothing
worn.

Athletes should aim to start training in a fully hydrated state. During the day, hydration
should be maintained by drinking water, fruit juices, squashes etc. Excessive amounts of tea
and coffee should be avoided

500 - 600ml water or sports drink (to maximise glycogen stores) should be consumed 2 –3
hours before exercise and then 200-300ml 10-20 minutes before exercise. Sports drinks are
useful before exercise if carbohydrate intake during the day has not been optimal or if there
has been a long gap between the last meal/snack and the training session or if the session will
be high intensity.

During training, 200-300ml fluids should be consumed every 10-20 minutes. These are
general guidelines but individual requirements should be calculated to avoid under or over
hydration

After training the fluid required to replaces losses should ideally be consumed within 2 hours
to ensure that optimal hydration is achieved as soon as possible in case a further event is
imminent.

The post exercise rehydration drink should contain carbohydrate to help replace glycogen
stores and sodium to help conserve water and encourage the drive to drink (i.e. an isotonic
or hypertonic sports drink)

Keeping the volume of fluid in the stomach at 600ml or more facilitates faster emptying and
absorption from the stomach and into the blood stream so hydration can keep pace with
sweat loss
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TYPES OF FLUID
It is important that athletes take fluid on board for any exercise lasting over 30 minutes.
Water may be sufficient for low intensity exercise up to 45-50 minutes. For higher intensity exercise
of 45-50mins where fluid losses are greater a sports drink would be of benefit.
An intake of 1g carbohydrate per minute maintains optimal carbohydrate metabolism – for example 1
litre of a 6% carbohydrate drink per hour of exercise. Generally athletes should choose an isotonic
(5-8% carbohydrate) sports drink unless training in very hot climates where large quantities of fluid
are required in which case a hypotonic (1-3% carbohydrate) sports drink may be more appropriate.
30-60g carbohydrate per hour in the form of a sports drink will maintain energy levels and enhance
performance. Preventing low blood glucose levels by consuming a sports drink can also be beneficial
to immune system function.
Cold fluids encourage greater consumption so a temperature of 10-15 degrees centigrade is
recommended for fluids.
SPORTS DRINKS
Sports drinks are fluids containing carbohydrate and electrolytes. The carbohydrate is usually a
mixture of glucose, sucrose, fructose and maltrodextrins (glucose polymers which are glucose units
linked together). High concentrations of fructose (>10%) can cause gastric upset and decrease water
absorption. The amount of fructose in a drink should be no more than 2-3g/100ml (2-3%).
The electrolytes added are sodium and sometime potassium and magnesium. Glucose absorption
requires the presence of sodium and is an active process, so the addition of sodium stimulates glucose
and water absorption. The provision of 22-30mmol (506 - 690mg) sodium per litre fluid would be
appropriate to replace most of the sodium lost from sweating whilst at the same time remaining
palatable. Sweat contains 40-80mmol sodium/l.
Drinks containing 5-8% glucose or sucrose are absorbed into the body more rapidly than water and
also provide some energy. A slightly higher concentration of carbohydrate can be used if the
carbohydrate source is a glucose polymer or maltodextrin, without decreasing the rate of stomach
emptying.
OSMOLALITY OF SPORTS DRINKS
An isotonic drink has the same number of dissolved particles as are found in plasma (about
290mosmol per kg). The dissolved particles are electrolytes and carbohydrates such as glucose or
glucose polymers. Isotonic drinks promote water and carbohydrate absorption.
A less concentrated drink containing 1-3% carbohydrate (hypotonic) has a lower osmolality and
promotes water absorption but provides less carbohydrate energy.
Drinks with a higher osmolality, usually >10% carbohydrate energy, are hypertonic and slow gastric
emptying thus decreasing fluid absorption. These more concentrated drinks are useful as recovery
drinks after exercise. They can also be used in situations when provision of fuel takes priority over
fluid replacement.
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EXAMPLES OF COMMONLY AVAILABLE ISOTONIC SPORTS DRINKS
Drink
Carbohydrate
(g) per 100ml
6
5.7
Energy
(kcal) per
100ml
25
22.8
Sodium
(mmol/mg)
per 100ml
1.8mmol/41mg
1.3mmol/30mg
Gatorade
SIS Go electrolyte
(powder)
Lucozade sport
Powerade
6.4
6
28
24
2.2mmol/50mg
2.2mmol/50mg
The composition of the powerade that will be available for the Olympic games has been modified to
contain 40g carbohydrate and 40mmol sodium per litre. This is to reflect the increase in sweat rate
and therefore sodium loss in a hot climate and is closer to the actual composition of sweat than most
sports drinks. The lower carbohydrate content is to take into account the fact that a greater fluid
volume will need to be consumed and so prevents excessive carbohydrate being taken on board
during exercise (30- 60gcarbohydrate per hour is the optimal amount to consume during exercise)
MONITORING
It is important that athletes monitor their own hydration status. They should be aware of the
symptoms of dehydration, of how to use urine volume and colour as an indicator of hydration status
and the importance of pre and post body weight measurements.
Signs and symptoms of dehydration include thirst, irritability, and general discomfort, followed by
headache, weakness, dizziness, cramps, chills, vomiting, nausea, head or neck heat sensations and
decreased performance
Thirst is a poor indicator of the need to drink to drink. Thirst indicates that 1.5-2.0l fluid have already
been lost
The ‘pee’ test. When fully hydrated large amounts of very pale yellow urine will be passed.
Numbers 1-3 should be the aim. Dark yellow urine is an indication of dehydration although vitamin
supplements containing riboflavin will colour the urine dark yellow.
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As discussed pre and post training weight can be used to calculate fluid losses. As a minimum, aim for
a body weight change of less than 2%.
Other tests that can be done in the field include urine specific gravity
URINE SPECIFIC GRAVITY MEASUREMENT
This is done using a refractometer and should be done using mid stream urine. This can be performed
by the physiologist or dietitian and gives a figure, which correlates to hydration status. See chart
below.
Indexes of hydration status
Condition
Well hydrated
Minimal dehydration
Significant
dehydration
Serious dehydration
% Body
weight
change
+1 to –1
-1 to –3
-3 –5
Urine
colour
Urine specific
gravity
1 or 2
3 or 4
5 or 6
<1.010
1.010 – 1.020
1.021 – 1.030
>5
>6
>1.030
% Body weight change = (Pre exercise body weight – post exercise body weight) x 100
Pre exercise body weight
HYPONATREMIA
A condition called hyponatremia can occur in athletes who consume excessive amounts of fluid or
who drink low sodium fluids. It is defined by low blood sodium levels less than 130mmol/l.
Hyponatremia occurs most frequently in sports lasting longer than 4 hours, during lower intensity
endurance activities, when athletes drink large volumes of water without adequate sodium intake.
Signs of hyponatremia are similar to those of heat stroke such as nausea, vomiting, extreme fatigue,
respiratory distress, and central nervous system disturbances (i.e. dizziness, confusion, disorientation,
coma and seizures). It also has unique characteristics such as low plasma sodium levels. Other
symptoms may include worsening headache, normal exercise core temperature (generally not >
104ºF), swelling of the hands and feet. If hyponatremia occurs medical help should be sought.
PREVENTION OF HYPONATRAEMIA
Athletes should be aware of the fluid replacement guidelines and should not replace fluids in excess of
sweat losses. They should have access to sports drinks containing sodium, monitor body weight and
aim not to gain weight during a training session. Consuming a little extra sodium during meals and
snacks during continuous days of training in a hot climate will also help maintain blood sodium levels.
FLUID INTAKE IN THE HEAT
Sweat rate increases after 10-14 days of heat exposure, so fluid intake should be increased
accordingly using pre and post weights to calculate sweat rate as previously discussed
General guidance for fluid replacement in the heat during training is 750-1250ml of sports drink per
hour but this should be adjusted for individuals
Increase sodium intake during the first 3-5 days of heat exposure as there is an increase in the
amount of sodium lost in sweat
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After 5-10days the sodium concentration of sweat decreases and normal sodium intake is sufficient.
If homemade sports drinks are used rather than commercial varieties then salt should be added to
these (1/4tspn -1.25g per litre) to ensure salt losses are replaced. This would equate to 500mg
sodium (sodium x 2.5 = salt).
To prevent taking on board excess carbohydrate, hypotonic (1-3%) sports drinks may be more
appropriate during exercise in the heat.
Keeping fluids chilled will encourage a greater intake.
Be aware of signs of dehydration and heat illness such headaches, nausea, vomiting, weakness,
dizziness. Confusion/disorientation and irrational behaviour can occur with heat stroke.
Useful references
National Athletic Association Position Statement: Fluid replacement for Athletes. J athletic training:
35(2): 212-224, 2000.
A USA Track and Field advisory. Proper hydration for distance running – identifying individual fluid
needs, 2003
Armstrong, L. E., Maresh, C. M., Castellani, J. W., Bergeron, M. F., Kenefick, R. W., Lagasse, K. E.,
Riebe, D.: Urinary indices of hydration status. Int. J. Sport Nutr. 4, 265-279, 1994.
Barr, S.I.: Effects of dehydration on exercise performance. Can. J. Appl. Physiol. 24 (2): 164-172,
1999.
Burke, L. M., Hawley J. A. Fluid balance in team sports. Sports Med. Jul 24 (1) 38-54, 1997.
Coombes, J. S., Hamilton, K. L. The effectiveness of commercially available sports drinks. Sports Med.
Mar. 29(3) 181- 209, 2000
Latzka, W. L.and Montain, S. J.: Water and electrolyte requirements for exercise. Clinics in Sports
Med. vol.18 no.3 July, 1999.
Maughan, R. J.: The sports drink as a functional food: formulations for successful performance. Proc.
Nutr. Soc., 57, 15-23, 1998.
Millard-Stafford M.: fluid replacement during exercise in the heat. Review and recommendations.
Sports Med. 13 (4): 222-223, 1992
Noakes T. D., Overconsumption of fluids by athletes. BMJ vol. 327 113-4, 2003.
Oppliger R. A., Bartok C. Hydration testing of athletes. Sports Med. 32 (15) 959-971, 2002
Shirreffs S.M. Markers of hydration. J Sports Med. Phys. Fitness March 40:80-4, 2000