Managing hydration to improve performance
BY Michelle Tolmay,
Registered Dietitian at Kings Park Medicine Centre
Why is hydration important?
When we exercise our body core temperate raises so we produce sweat to help cool us down. Sweat contains water and electrolytes which need to be replaced otherwise dehydration and hyponatremia (low blood sodium) can develop. The higher the temperature the more we will sweat and the higher the fluid and electrolyte requirements are. Long duration exercise in hot climates will increase the risk of dehydration which will negatively impact performance and lead to medical problems.
Monitoring hydration
We can monitor your hydration by checking weight. measure your baseline body weight on waking before eating/drinking, with minimal clothing and having gone to the bathroom. To
determine fluid loss check your weight after training (before eating/drinking, after going to the toilet and with minimal clothing).
Exercise performance is impaired when 2% or more of body weight is lost through sweat. Weight loss of more than 4% body weight may lead to severe dehydration and possible
death. Measuring pre and post exercise body weight during training will help perfect your fluid replacement strategy for competition.
Complications of dehydration
Heat exhaustion and heat stroke
Rahabdomyolysis (syndrome causing release of skeletal muscle contents) associated with acute renal failure
Dehydration with low sodium can lead to muscle cramps
Tips for managing hydration
Before Exercise
For the days leading up to an event:
Consume sufficient beverages with meals, including salty food.
Have a recovery period of 8-12 hours after the last exercise session.
Aim to drink 6 mL of fluid per kg of body mass every 2–3 h, as well as 2–3 h before training/competition in order to start exercise normally hydrated.
Urin colour should be a light yellow and not dark and concentrated.
During Exercise
Use a fluid intake plan that has been practiced allowing a comfortable, practical drinking rate that replaces your individual fluid loss.
An example is to drink according to thirst from 400 to 800mls per hour (higher rates for faster, heavier individuals in warm environments and the lower rates for the slower, lighter persons in cooler environments).
Start fluid replacement early and drink at regular intervals according to a fluid replacement program (e.g. every 30min)
Plan to replace sodium through sports drinks and food. the aim os 0.5-0.7g per Litre of fluid for exercise longer than one hour.
Include a diluted carbohydrate (CHO) & electrolyte drink to aid fluid absorption in the gut as well as replace energy. The aim is 30-60g of CHO per hour for exercise longer than one hour, and up to 90g CHO per hour for exercise longer than 2.5 hours.
Plan to replace sodium through sports drinks and food.
Drink cold beverages (10–20°C) to optimise thermoregulation during exercise.
After Exercise
The goal after exercise is to replace any fluid and electrolytes lost.
The recovery hydration regime should include sodium, protein and CHO. Drinks such as chocolate milk is recommended as it contains a 4:1 CHO-protein-ratio as well as sodium.
If time permits, consumption of normal meals and beverages will restore normal hydration.
Individuals needing rapid and complete recovery from excessive dehydration can drink ~1.5 L of fluid for each kilogram of body weight lost.
*For more information contact Michelle Tolmay (RD) at:
Kings Park Sports Medicine Centre
892 Umgeni Road, Morningside Durban
031 303 3874
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