How hydrated are you?

With the hottest days of summer just around the corner, and with so much of your focus on your training, how much time do you spend thinking about your hydration? If you haven’t been thinking about it, you should know that hydration will profoundly affect performance and health more than any other factor.

It has been shown that even a 1-2% drop in bodyweight as a result of fluid loss will contribute to decreased performance and increased health risks. In conditions where heat plays a role, the risks ultimately may include death.

When exercising, the average person will lose approximately 1-2 litres of sweat per hour depending on level of exertion, environmental factors, body size, and whether or not you are a profuse sweater. If you are able to weigh yourself before and after a workout (both without clothes since they will hold on to sweat), whatever the difference is represents what you need to replace. For example, if you weighed 1 kilogram (2.2 lbs) less at the end of a 60 minute run (1 kg is equal to 1 litre of water), you could have replaced the lost fluid with 250ml of water at the 15, 30, 45, and 60 minute mark of your workout to avoid dehydration (providing you weren’t dehydrated to begin with).

Here are the top 10 tips to avoid dehydration:

1. To stay hydrated, you should be aiming for a minimum of 2-3 litres of water per day, and 3-4 litres if you are active, and as much as 10 litres at the upper limit (an extreme exerciser and profuse sweater).
2. Drink 400-600 ml of fluids two hours prior to starting exercise to delay dehydration and allow time to excrete excess water.
3. Consume cool drinks (4-5 degrees Celsius) as people consume more than when they are warmer.
4. Drink constantly in small amounts rather than waiting and trying to consume a single large amount of fluids.
5. Drink to replace what you are losing, so drink more when you are sweating more, and less when you are sweating less.
6. Fluids that have a carbohydrate composition of no more than 7% will optimize the speed at which fluids leave the stomach and are absorbed by the body. 7% equals about 70 grams per 1 litre of liquid (most sport drinks have about 5-6% carbohydrate compared to cola’s 19%). More than 7% may slow rehydration.
7. If you are consuming a lot of fluids, especially during exercise that lasts longer than 1 hour, they should contain electrolytes to decrease the risk of hyponatremia (a potentially dangerous condition whereby a person does not have enough sodium in the bodies). As sodium is the most important electrolyte, aim for .5-.7g of sodium per litre of fluid.
8. Be careful that you don’t underestimate fluid loss when you don’t feel like you are sweating (i.e. cycling, whereby your sweat evaporates before you feel it)
9. Favouring should be light to avoid “flavour fatigue”, whereby you stop consuming your fluids because you get sick of the taste, especially common in long-distance and ultra-endurance activities (typically longer than 4 hours).
10. Remember that those other “beverages”, especially the alcoholic ones do not count towards your hydration needs and may contribute to dehydration.

References:

American College of Sports Medicine (1996). Position stand on exercise and fluid replacement. Medicine and Sciencein Sport and Exercise. 28:i-vii.

Casa, DJ, et al. NATA Position Statement: Fluid Replacement For Athletes (2000). Journal of Athletic Training. 35:212-224.