As a group exercise instructor and a bicyclist, I can be physically active up to 2-3 hours/day and staying hydrated is incredibly important. Furthermore, with the increasing number of people exercising outdoors as higher summer temperatures approach, it seemed fitting to write a blog on staying hydrated while exercising.

While we produce heat and sweat naturally during exercise, hot outdoor temperatures increase sweat production, leaving us more likely to become dehydrated while exercising outdoors. Dehydration disturbs water and electrolyte balance and decreases blood volume and cardiac output, all which negatively affect physical and mental athletic performance. Dehydration can also cause heat exhaustion or even heat stroke and causes stress to the organs. Symptoms of dehydration include thirst, dizziness, headache, fatigue and cramps as well as other undesirable symptoms.  

Hydration guidelines for exercising


·         4 hours before exercise, take in 5-7ml/kg (approx. 2-3mL/lb) of water. As a guideline, a  165lb (75kg) person would need to consume about 375-525mL of water, about 1.5-2 cups.

·         If not properly hydrated and urine is dark in colour, take in an extra 3-5mL/kg          (approx. 1.5-2.5mL/lb) of water over the course of 2 hours before exercise. This would equate to about 1-2 cups for a 165lb person.

During exercise:

·         Take in 2-8 cups (1/2-2L) of water/ hour during activity in order to counter sweat loss from exercise. The amount of fluid required varies with the weather, chosen sport, exercise intensity and the individual person. A great way to meet hydration needs (in most cases) throughout exercise would be to have approximately ½ cup (or 4 gulps) of water at every 10-15 minute interval during intense exercise.

After exercise:

·         For many of us, drinking 1 or 2 cups of water after exercising and having a snack and a meal is enough to restore hydration. If in training for an event or a tournament of if training more than 2x/day, it is important to drink 16-24 oz (2- 3) cups of fluids after exercise for every pound of body weight lost during activity.  Athletes often weigh themselves before and after exercise to find out their fluid needs.

To find out more information or to learn about electrolyte (and carbohydrate) intake during exercise lasting longer than 1 hour, contact me at

Nicole Marchand, RD

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