Sport + Hydration
Sweating is important during activity because it helps control your body temperature and prevent overheating. But, when you sweat, your body loses water and electrolytes (mainly sodium) that need to be replaced in order to replenish blood volume and prevent dehydration. Even minor dehydration can cause fatigue, nausea, headaches, muscle cramps, decreased ability to concentrate, and ultimately impair performance and health.
How much should I drink?
Don’t start your activity dehydrated before you even break a sweat…
- 4 hours before: drink 250-500ml (1-2 cups).
More specifically: 5-7ml for every kg of body weight.
Ex., if you weigh 70kg, that would be 350-490ml.
- 2 hours before: if you have not yet urinated (or if your urine was concentrated), drink an extra 125-375ml (0.5 – 1.5 cups).
More specifically: 3-5ml for every kg of body weight.
Ex., if you weigh 70kg, that would be 210-350ml.
Remember to allow enough time for a bathroom break before you start exercising. No one wants to be jumping around with a full bladder!
Sweat rates are very individual and can range from ~300-2400mL/hour. You will sweat more in high temperatures/humidity and during more intense activity. The goal is to drink enough fluid to replace sweat losses.
Because sweat rates are so variable, a good starting point is to drink 400-800ml per hour of activity (0.5 - 1 cup every 20 minutes or so) and make adjustments from there.
To personalize fluid replacement during sport, you can estimate your hourly sweat rate by measuring your weight before and after activity to see how much fluid weight you’ve lost. Then add on the fluid you drank and subtract any urine losses. Note that 1lb (0.5kg) of body weight is equivalent to ~500ml (2 cups) of fluid. A Registered Dietitian can help you estimate your hourly sweat rate and make custom recommendations for fluid replacement during sport.
After activity the goal is to drink enough fluid to replace any excess sweat losses that are still remaining. This is especially important if you have limited recovery time before your next training session or sporting event. If you were able to drink enough during activity to keep up with your sweat rate, you may not need to drink much extra fluid afterwards.
You can weigh yourself before and after activity, and drink 500-750ml (2-3 cups) per 1lb (0.5kg) of body weight lost. Aim to do this within 4-6 hours after completing your activity.
What should I drink?
A) PLAIN WATER:
- for activities lasting an hour or less
Feel free to flavor water with lemon or lime or whatever your heart desires to encourage yourself to drink more – it’s been proven to help!
B) WATER + ELECTROLYTES (mainly sodium):
Ex: sports drinks (like Gatorade) or water with added electrolyte tabs/powders
- for activities lasting longer than 2 hours
- if you are exercising in hotter temperatures than usual
- if your personal sweat rate is greater than 1.2L/hour
- to replace large sweat losses that remain after activity (alternatively, you could drink plain water along with sodium-containing foods such as pretzels, crackers, pasta sauce, etc.)
For activity lasting longer than 1 hour, it is important to eat or drink some form of carbohydrate for energy. So your fluid choice could be plain water if you also EAT carbohydrates (ex: sport gel, fruit, jam sandwich, etc.); or it could be a sports drink or watered down juice if you choose to DRINK your carbohydrates instead.
Fluids to avoid during activity:
· full-strength fruit juice or fruit cocktails,
· pop, energy drinks, or vitamin waters
These fluids contain too much free sugar and may cause stomach upset, diarrhea, and even impair fluid absorption.
What about caffeine?
Caffeine has been shown to enhance performance by stimulating the central nervous system. It can make exercise feel easier and delay the sensation of fatigue. Caffeine is found in coffee, tea, chocolate, some herbs, select sports drinks and gels, and can also be taken as a supplement. Caffeine affects everyone differently, so it is important to trial the effects of caffeine in a training setting, before using it in competition. Aim to consume 1-3mg of caffeine per kg of body weight an hour before or during lengthy activity. For most people, this would be equivalent to ~1 cup of brewed coffee.
How do I know if I’m getting enough?
A) CHECK OUT YOUR PEE:
Aim for lots of pale yellow urine (lemonade color) versus a small amount of the concentrated urine (apple juice color). Be aware that vitamin supplements can produce bright yellow urine even if you are well hydrated.
B) WEIGHT YOURSELF BEFORE & AFTER SPORT:
If you lose more than 2% of your body weight during exercise, you are likely not drinking enough during activity. For example, if you weigh 135lb and lose more than 2.7lb, you need to drink more.