Hydration in sport

60% of body weight is water.  Water within the body has several functions:

  • It is a coolant and helps to reduce body temperature – 75% of energy is in the form of heat
  • It is a carrier for nutrients and cells 
  • It aids in the removal of waste from the body, dilutes toxins in blood and makes them less toxic
  • It is required for chemical reactions to occur
  • It enhances joint lubricants including synovial fluid and cerebro-spinal fluid
  • It provides a medium for electrolyte minerals (sodium, potassium, calcium, chloride and magnesium) to be carried and aids in the stimulation of nerves and contraction of muscle

Water can be lost through several means including urine, sweat and faeces.  The body’s drive to drink is not as powerful as it’s drive to eat, by the time the thirst mechanism sets in there is already 1-2 % dehydration.  Dehydration has many effects upon the body’s ability to function and certainly within a sports environment it can have profound effects. 

3% dehydration can lead to 10% loss of performance.  2-4% dehydration can lead up to as much as a 21% reduction of strength training function and up to 48% reduction in aerobic function.

The symptoms of dehydration include:

  • Dry mouth
  • Dry cough
  • Hoarse voice
  • Headaches
  • Reduction in urination
  • Muscle cramps
  • Heat exhaustion
  • Reduced mental function
  • Hallucinations
  • Long term dehydration can increase the risk of cancers (breast, prostate, testicular, bladder, kidney, colon).  This may be due to the fact that water has a flushing action and this may help to dilute toxins that may be carcinogenic.

The effects of dehydration are most noticeable when exercising in a humid environment or at high altitudes.

Monitoring hydration

The amount of water lost through sweat is dependant upon the level of exercise undertaken.  A good way to calculate your fluid loss is to weigh yourself prior to exercise and after exercise and deduct the post-exercise weight from the pre-exercise weight.  Each kilo of weight lost is equal to approximately 1 litre of water lost.  Ideally you should drink 1˝ litres of water for each kilo of weight lost.   If you are properly hydrated you should urinate every 2-3 hours and your urine colour should be pale yellow and have no odour

Normal daily fluid requirements are estimated at 35ml /kg.  Most athletes will require 2-3 litres a day, not including fluids lost through sweating.

To calculate your requirement multiply 35 by how many kg you weigh and divide by 16.  This will give you your hourly requirement taking into account an 8-hour sleep period.

RECOMMENDATIONS:

  • Drink at regular intervals –every day, especially during exercise
  • Drink according to your environment – Extreme conditions hot or cold create and increased need for water
  • Keep fluids slightly cooler than ambient temperature as this aids in fluid replacement
  • Always take a drink bottle to training sessions
  • For exercise less than 1 hour plain water is adequate
  • For exercise over 1 hour a sports drink is recommended
  • During exercise AVOID fruit juices, sodas, alcohol, carbonated drinks and sports drinks with over 8% carbohydrate.
  • Avoid alcohol after large events or strenuous exercise as this has a dehydrating effect

Sports drinks

Sports drinks are used to enhance the uptake of water, provide carbohydrates and to replace minerals.  Some commercially available sports drinks have considerable amounts of aspartame and other artificial chemicals that are best avoided. 

There are 3 types of sports drinks isotonic, hypotonic and hypertonic.

It is easy and cost efficient to make your own rehydration fluid:

Isotonic – 6-8% carbohydrate – 200ml fruit squash, 800ml of water and a pinch of salt

Hypertonic – high level of carbohydrate - 400ml squash, 1 litre of water, pinch of salt

Hypotonic – low level of carbohydrate – 100ml fruit squash, 900ml of water and a pinch of salt

In general, unless you do heavy exercise for long periods of time, an isotonic sports drink will provide adequate water and nutrient replacement. 

So, next time you head out the door for your long Sunday morning run don’t forget to take plenty of fluids with you!