Staying hydrated is essential for everyone, but people who play sport and exercise regularly have an even greater need to maintain proper hydration. The side effects of poor hydration on performance can include:
- increased heart rate
- impaired heat regulation
- increased perceived exertion
- reduced mental function
- reduced skill level
The hydration zone
When it comes to hydrating during sport and exercise, the goal is to avoid gaining weight (a sign that you’ve consumed too much fluid) and avoid losing more than 2% of your pre-exercise body weight (which is the level of fluid loss beyond which performance is affected). This is the hydration zone, where individuals perform at their best and avoid the adverse health effects of dehydration or over-hydration.
What is a sweat rate?
The way to stay in the hydration zone is to consume fluids at a rate that keeps pace with your sweat rate. Fluid needs vary based on factors such as body size, exercise intensity, and competition conditions. That means that everyone will have their own unique sweat rate, so it is best that you calculate your individual sweat rates for the various conditions in which you train or compete.
Basic sweat rate testing
You can easily estimate your fluid requirements by weighing yourself before and after training or games. Each kilogram (kg) of weight lost is equivalent to approximately one litre (L) of fluid.
- Weigh yourself before training (Initial Weight)
- Weigh yourself after training (Final Weight)
- Subtract Final Weight from Initial Weight.
- The difference plus the volume of fluid consumed during training gives you your sweat rate for that period of time.
- Divide this by the total time (hours) to determine hourly sweat rate.
- Aim to match fluid intake to sweat rate
Sweat Rate (L/hr) = [Initial Weight (kg) - Final Weight (kg)] + Fluid (L)/Time (hrs)
What is the best drink during sport?
Water is cheap and effective for hydration in low intensity or short duration workouts (less than one hour). A sports drink is ideal for longer sessions and where sweat losses are high (e.g. when training in hot or humid conditions).
Sports drinks provide carbohydrates to top up fuel levels during exercise and electrolytes such as sodium and potassium which help you retain more fluid and replace the electrolytes lost in sweat.
Rehydration after sport?
After training or a game, replacing fluid plus electrolyte losses is important for optimal recovery. You continue to lose fluid through sweat and urine even after finishing your session, so you should aim to replace losses by 150%. In practice, this means if you are 1 kilogram lighter after your workout, you need to drink 1.5 litres over the next 2-6 hours.
Including a protein source after exercise is also important for repairing muscle tissue. Milk naturally contains fluid, electrolytes and high quality proteins, and has been shown to be as effective if not more effective for rehydration than water or a sports drinks.