Dehydration is arguably the greatest risk faced by bushwalkers
in Western Australia, and fluid mis-management can easily
create a life-threatening situation. Water availability
in many of Western Australia's premier walking areas may
be continuously or seasonally scarce, and close attention
to water availability and drinkability in the walking
area - at the time of the walk - is essential.
The following is some information on exercise and fluid
replacement - not specifically for bushwalking but good
general information. It is adapted from the American National
Athletic Trainers Association (NATA), making reference
to their position statement on 'Fluid Replacement for
Athletes', and the American College of Sports Medicine
(ACSM), one of the leading authorities on safe, effective
exercise. These recommendations are primarily for those
who exercise on a regular basis, but should be adhered
to whenever you exercise.
Remember, we are all different and we have different
requirements. These are recommendations and guidelines
only; if you are on any medication or are recovering from
an illness or injury, make sure that you discuss any concerns
you may have with your doctor before embarking on an exercise
routine.
Why Do We Need to Drink When We Exercise?
There are a number of reasons why we should drink plenty
of fluids while exercising:
-
When we sweat, the water we lose comes from blood plasma.
By drinking prior to and during exercise, we prevent
a decrease in our total blood volume. This decrease
in blood volume is known as 'dehydration', and if you
become dehydrated your capacity to carry oxygen to the
cells that need it is reduced and you will tire more
quickly.
-
Staying hydrated also helps to maintain the balance
of fluid and electrolytes in the cells. Mild dehydration
(loss of <2% body weight), however, is generally unavoidable,
as athletes cannot always replenish fluids at a rate
equal to those being lost.
-
Drinking during exercise helps to maintain optimal performance,
as research has shown that a decrease in body fluids
can significantly decrease physical and mental performance.
Dehydration causing loss of only 2% body weight (1.5kg
in a person weighing 75kg) has been found to impair
temperature regulation and reduce endurance capacity
and aerobic performance.
- Taking on fluid while exercising helps
to regulate body temperature.
How Much and How Often?
Both the ACSM and NATA have comprehensive guidelines regarding
both the recommended amount of fluid and the composition
of that fluid. These guidelines can be found on their
websites - www.acsm.org and
www.nata.org - but the following
is a brief summary of their recommendations.
It is recommended that for optimal performance, individuals
should eat a nutritionally balanced meal about 24 hours
before exercising and drink adequately. It is also extremely
important to drink plenty of water - about 500ml - during
the last meal before you exercise, which is generally
eaten at least two hours beforehand. During exercise,
you should also sip small amounts of fluid regularly to
maintain fluid balance. This optimal hydration can be
achieved by drinking 150-350ml of fluid at 15-20 minute
intervals from the start of your exercise routine and
throughout. Take small, regular sips from your water container,
and make sure it is big enough to enable you to continue
to exercise without too much interruption. It is also
very important to continue re-hydrating after your exercise
session. Aim to be re-hydrated between one to two hours
after exercise.
Obviously, the amount of fluid that should be consumed
by each individual depends on a number of factors, such
as:
-
The length of time you spend exercising.
-
The intensity, i.e. how 'hard' the exercise session
is.
-
Your body size.
-
The environment you are exercising in. When we exercise,
our internal body temperature increases due to the build
up of heat in the muscles. We generally cool ourselves
down by perspiring. The evaporation of this sweat from
our skin helps us to maintain a lower core body temperature.
This process of perspiration and evaporation is more
efficient in certain environments/climates. For example,
when there is high humidity, less evaporation takes
place, therefore to keep our internal body heat down
we may need to drink slightly more and decrease the
intensity of our exercise. Be aware that even while
exercising indoors with the air conditioning on, you
can still become dehydrated.
-
How your body temperature responds to exercise. Obviously,
the more you sweat, the more fluid you need to replace.
Some highly trained athletes have been recorded to sweat
up to three litres/hour and 15 litres/day (that's around
20% of body weight in one day)!
How Do We Know if We are Drinking
Enough?
One way to find this out is to check the colour of your
urine. If your urine is clear or straw-coloured, rather
than yellow, you are sufficiently hydrated. However, it
is important to remember that some vitamin supplements
may affect the urine by turning it yellow, thereby possibly
giving a false or confusing impression. Also, if you can
weigh yourself before and after a workout, a good rule
of thumb is to drink one litre of water for every kilo
you've lost.
Do not wait until you are thirsty before you drink! When
we feel thirsty and are in need of a drink, we are already
dehydrated.
What Should We Drink?
For many years there has been a great debate about what
we should drink from our fluid bottles. It is recommended
that in events lasting less than one hour, water is appropriate.
In intense events lasting more than one hour, drinks containing
carbohydrate in concentrations of 4-8% and/or electrolytes
(sodium and potassium) are recommended. These drinks can
be used for shorter, less intense sessions, but they are
not considered to be necessary.
What is Over-Hydration?
It has been found that a steady source of carbohydrates
during exercise in the form of a carbohydrate drink fights
off fatigue and enhances performance by fuelling the muscles
during exercise. It is also recommended that fluids should
be cooler than ambient temperature, between 15º and
22ºC and flavoured to enhance palatability and thus
promote fluid replacement.
It is also suggested that sodium (salt) is added to the
re-hydration fluid if the activity lasts longer than one
hour, because it helps to promote fluid retention and
can prevent a condition referred to as hyponatraemia.
Hyponatraemia can occur when blood-sodium concentrations
of less than 130mmol/l are present. These low blood sodium
concentrations develop either as a result of prolonged,
heavy sweating with failure to replace sodium, or from
drinking too much water during prolonged exercise.
Although most athletes who drink more fluid than they
lose as sweat simply excrete the excess fluid as urine,
in a few people it is retained. It is uncommon for athletes
to suffer from hyponatraemia or over-hydration but it
does happen. For example, 11 of 605 athletes entered in
the New Zealand Ironman Triathlon developed severe hyponatraemia,
and it was suggested that eight of these athletes were
over-hydrated, as they had either maintained or gained
up to 5% of body weight during the race.
Sports Drinks
There are many sports drinks on the market nowadays containing
both carbohydrate and electrolytes, but because most commercial
sports drinks do not contain enough sodium to optimise
post-exercise fluid replacement, it is recommended that
athletes re-hydrate in conjunction with a sodium-containing
meal. High-sodium items include soups, pickles, cheeses,
processed meats, pizza, pretzels and popcorn. Use of condiments
such as soy sauce and ketchup, as well as salting food
at the table, can also increase our sodium intake. Obviously,
it is imperative from a healthy heart perspective that
you limit your sodium intake when you are not planning
to exercise.
If you fail to follow these guidelines you can leave
yourself wide open to serious health complications.
