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.
