Just like our bodies need fuel to function at their best, fluids are equally as important. The average adult needs approximately 2-3 litres (9-12 cups) of fluids every day to stay hydrated. Physical activity can increase needs depending on the exercise you do, the intensity, the weather and your individual sweat rate. You could lose anywhere from 0.3 to 2.4 litres (approximately 1 to 10 cups) of sweat per hour based on these factors. If these losses are not replaced you could be left feeling tired, overheated and unable to exercise to the best of your ability.
Severe dehydration can lead to an increased risk of heat-related illness and heat stroke so it's important to be able to spot the signs of dehydration and address them as soon as possible. Signs include thirst, dizziness, headache and muscle cramps. Check the colour of your urine to ensure you're not dehydrated before and after exercising; pale yellow signifies adequate hydration, while a dark yellow, apple juice colour could mean you're dehydrated.
One way to determine your fluid losses during exercise is to weight yourself just before and right after physical activity. Remember to empty your bladder and remove any sweaty clothing before weighing. If you lose more than two per cent of your body weight during exercise, it means you need to drink more than your 2-3 litre per day requirement. Remember that weight loss immediately following exercise is water loss, not fat loss.
Water is the best option for replacing fluid losses but sports drinks can be useful following intense exercise, activities lasting longer than an hour, when working out in hot weather or when wearing heavy sports equipment, such as in hockey. In these situations, fluid losses can be greater and contribute to an increased need for electrolytes (primarily sodium and potassium). The carbohydrates in sports drinks can also help to provide a source of energy during intense exercise.
Sweat rates and sweat sodium concentrations can vary between individuals. Athletes with a high sweat rate (greater than 1.2 litres per hour), salty sweat or those exercising for more than two hours may want to think about including sodium, or salt, in their fluids during exercise. Unless you're working-out at a high intensity or for an extended period of time (greater than two hours) it is not necessary to supplement with additional potassium.
An example of a homemade sports drink with a good balance of both sodium and potassium would include 500mL apple juice, 500mL water and tsp. salt.
Try to avoid carbonated soft drinks, energy drinks, full-strength juice and fruit drinks during exercise, which can all be too high in sugar, drawing water into the digestive system and hindering absorption. The body can only absorb fluids at a rate of 10-15mL per kilogram of body weight per hour so be sure to sip your fluids throughout the day, and during exercise, rather than gulping them down.
Dietitians of Canada also has several recommendations for how much fluid you need to drink to stay hydrated during exercise:
1. Four hours before exercise, drink 250-500mL (1-2 cups) of fluid.
2. Two hours or less before exercise, drink 125-375mL ( to 1 cups) of fluid if you're showing signs of dehydration such as dark-coloured urine.
3. During exercise, sip fluid during your activity but avoid gaining weight during exercise, which can be a sign of overhydration.
4. Immediately after exercise, drink 500-750mL (2-3 cups) of fluid per 0.5kg (1lb) of weight lost. If you were sipping throughout your workout and did not lose any weight, it is not necessary to drink additional fluids post workout.
-- Kelsey Leckovic is a Registered Dietitian with Northern Health working in chronic disease management.
