Hydrating for Activity

Water – the chemical compound of H20 (two hydrogen atoms bound with one oxygen atom) is the basis for life. It is second only to oxygen in importance for health, making up to 75% of the body. Every cell depends on water to perform essential functions. Although water does not provide a source of calories, adequate hydration is at least as important to good athletic performance as the food you eat and is essential for efficient training, playing and racing.

What is hydration, and why is it important to my health?
Hydration is the replacement of body fluids lost by the body each day through the processes of sweating, exhaling and elimination.

Proper hydration not only quenches one's thirst but allows the body to flush toxins, maintain system equilibrium (balance), support brain function, hormone balance, metabolic processes (including fat metabolism), the transportation of life-giving vitamins and minerals and supports the integrity of muscle, joint and bone in our bodies.

Minimum fluid consumption
Although the human body can, in extreme cases, go without food for up to six weeks, it can only survive a week without water. As a general rule, it is recommended that the 'average person' consume at least eight 8-ounce servings of water each day (2 litres/day). The more time you spend outdoors, and the more active you are, the more water you need to replenish lost fluids.

How do I become dehydrated?
The human body loses fluids through perspiration (sweat), exhalation (breathing), and elimination (urine). During exercise, the body keeps cool by circulating blood to the skin, where water is lost from the blood in the form of sweat. When sweat evaporates, it cools the skin. This in turn cools the blood that is carried to the body core. The environmental conditions (temperature, humidity, etc.) in which an active person trains or competes will have a direct effect upon their fluid equilibrium. Generally, the hotter it is, the more you sweat.

How can I tell when I'm dehydrated?
One of the easiest ways to tell whether you are adequately hydrated is by checking the colour of your urine. In general, light coloured urine is an indication of adequate hydration. If you are experiencing infrequent urination and the colour of the urine is dark yellow, these are signs of dehydration.

Other signs of dehydration are: thirst, headache, constipation, fatigue, weakness, dizziness, irritability, cramps, depression, weight, gain, water retention, skin blemishes, vomiting or nausea, and bladder infections.

If an athlete becomes dehydrated but is still mentally alert and has no gastrointestinal (GI) pain, then s/he can re-hydrate orally. But, if the athlete has lost consciousness, has become confused or is suffering GI pain, s/he needs to be transported immediately to an emergency medical facility.

Tips for proper hydration:

  • Start and end your day with a 250 ml (8 oz) serving of water. Your body loses water while you sleep, so drink a serving before bed and again when you wake up.
  • Drink before you are thirsty. By the time you feel thirsty; you have probably already lost two or more cups of your total body water composition. Drink plenty of water throughout the day. Carry a bottle of water with you daily. Keep a bottle of water on your desk and refill at the office water cooler reguarly.
  • Don't substitute with alcoholic beverages. Alcohol is a diuretic and will cause you to lose water through increased urination.
  • It is important to note that although coffee and tea do have a diuretic effect, they do provide a significant amount of fluid and any effect of caffeine on urine losses are minor (especially for habitual caffeine users).
  • Keep drinking water even when it is cold outside. You may not feel thirsty as you do when it's hot, but you are still going to lose water through perspiration. You also lose fluids through exhaled air. When cold, dry air is inhaled, it is warmed and moistened in the lungs and exhaled as humid warm air. This process makes intense demands on the body's water supply.
  • Average sweat rates can vary from 0.5L/hour to more than 2.5L/hour. Knowing your sweat rate will help you to better prepare for both training and competition. Calculate your sweat rate. Taking the time to calculate how much you sweat is a fundamental consideration for optimal hydration.


SWEAT RATE = weight before workout – weight after workout + volume of fluids consumed (1 cup = 1/2 lbs)

  • weigh yourself in minimal clothing
  • towel off sweat
  • avoid urinating until after post-workout weight


  • Add sodium in rehydration beverages if; you have not eaten, if your workout is going to last more than 4 hours, if you are training in hot weather. Under these conditions, adding modest amounts of salt to the beverage can offset salt loss and minimize problems associated with electrolyte imbalance (such as muscle cramps). Adding a 1/4 tsp to L of fluid may help replenish sodium losses.

Hydration Prior to Exercise
Begin all workouts well hydrated. The following quantities are recommended.

  • Drink 450-650 ml (15-20 ounces) of water or sports drink 1 to 3 hours before exercise. (An additional 200-300 ml (7-10 ounces) consumed 10-20 minutes prior to the training session is also good practice).

Hydration during exercise
Don't stop drinking. If possible, given your sporting activity, take regular 'sips' throughout the activity.

  • Drink 200-350 ml every 15-20 minutes.

Get technical. For longer training sessions (or in hot weather) consider using a sports drink as part of your hydration regimen (prior to, during and following activity). The sodium and potassium content in most sports drinks will permit you to maintain a proper electrolyte balance.

Hydration following activity
Replace it all with the good stuff. You should aim to 'push' fluid intake even if you don't feel thirsty. Given that you will eliminate some fluid through urination, you will want to drink more than what you've lost.

  • Drink 500-1000ml (16-24 ounces) within 1 hour post exercise.

Can I drink too much?
YES you can! While most athletes understand the importance of proper hydration, most do not realize that overhydrating can dangerously lower blood sodium levels; a condition known as hyponatremia or "water intoxication". Athletes (such as ultra-marathoners and triathletes who sweat are training and sweating over many hours, and may drink primarily water during an event) can take in too much water and cause electrolyte imbalances which may lead to seizures, coma and even death.

When asked about hyponatremia, Dr. Paul Watson, sport medicine physician from Duncan BC, said "Clearly, hyponatremia is more common than we thought. Not simply over-hydration, but an interaction between the nervous and endocrine systems, it is a problem of the water preservation system of the body. Each of us responds to exercise in all sorts of ways, and our bodies don't accommodate well, if untrained, to certain environmental conditions. Although we now know more about the sugar, sodium and potassium content in sports drinks, we still don't know enough." The underlying message Dr. Duncan shares with us is that you must "know your body, know your sweat rate under various conditions, and prepare accordingly."

Ultimately, hydration is not simply a question of drinking fluids, but of knowing your own body and drinking the right fluids for you and your various activities, in various environmental conditions.


Burke, L., (2007). Sport Foods and Supplements. Practical Sports Nutrition (pp. 60). Human Kinetics. Champlain.

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