Q ) How do I calculate my fluid requirements?
Before exercise
Goal:
To start the event fully hydrated with normal blood
electrolyte levels.
- Individuals should drink beverages slowly (5-7ml per kg of body weight) at least 4 hours before exercise. For example: a person weighs 70.0 kg, therefore they should drink between 350 ml to 490 ml. If the individual does not pee he/she should drink an additional (3-5ml per kg of body weight) about 2 hours before the event.
- If you are training early in the morning drink as much fluid as is comfortable (300-500ml), about 10-15 mins prior to training
- Hydrating before the event allows urine output to return to normal.
- Consuming drinks with some sodium or sodium containing foods, will help stimulate thirst and retain the fluids that have been consumed.
Drinking during the event
Goal:
To prevent excessive dehydration and changes in your electrolyte balance and maintain optimal performance
- Aim is to prevent losing more than 2% of body weight due to fluid loses. Greater than 2% can negatively impact on aerobic performance & degrade mental and cognitive performance.
- Calculating sweat losses for a 70 kg athlete exercising for 2 hrs:
| Weight before exercise - Weight after exercise |
= sweat loss |
| Example: 70.0 - 68.5 |
1.5 kg or 1.5 Litres |
| % body loss: 1.5/70 x 100 |
2.1 % |
An athlete can use this as a guide for how much they should aim to drink during similar competition or training session in similar environmental conditions.
The above athlete needs to drink 1500 ml (1.5 L) of fluid to fully replace their sweat loss. If the session is over 2 hours the athlete will attempt to drink 200-250 ml every 15 mins. (Women typically have less sweat losses and electrolyte losses compared to men- they have a smaller body size & lower metabolic rates)
- CHO based sports drinks can be used to meet CHO needs, replace sweat and electrolyte losses (see section on sport nutrition for CHO guidelines)
- Care should be taken in deciding fluid requirements in events lasting greater than 3 hours. It is important not to drink too much and that intake matches sweat losses. It will also be important to determine the sodium content of the fluids being consumed. Consult a sports Dietitian if specific advice is required.
After exercise
Goal:
To fully replace any fluid and electrolyte losses and to restore fluid balance you need to drink 1.5 times the amount of body weight loss. This will account for the continued sweating that occurs after you have finished exercising.
| Weight before exercise - Weight after exercise |
= sweat loss |
| Example: 70.0 - 69.6 |
0.4 kg or 0.4 L |
| Sweat loss x 1.5 |
amount to drink |
| 0.4 L (400 ml) x 1.5 |
0.6 L (600 ml) |
To restore fluid losses the above athlete needs to drink:
600 ml |
- Consuming drinks & food with sodium will aid recovery, by stimulating thirst and fluid retention
- Alcohol consumption can increase urine output and delay full re-hydration. Consume in moderation or not at all until your are fully re-hydrated.
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