We all know that when we work out we sweat and loose bodily fluids, this loss in fluids can have an impact on how we perform. Did you know studies have found that athletes who lose as little as two percent of their body weight through sweating can have a drop in blood volume which causes the heart to work harder to circulate blood.
A drop in blood volume may also lead to muscle cramps, dizziness, fatigue and heat illness including: heat exhaustion and heat stroke. With dehydration potentially having such serious effects it is important to know what causes dehydration and how to prevent it.
Common causes of dehydration
Dehydration is defined as losing 2 percent or more of your body’s weight in fluid. As I have already mentioned being dehydrated can have serious effects and is best avoided. It is uncommon for those people who exercise for under 1 hour to suffer from dehydration but if you train for more than an hour you are at risk.
Some of the reasons you can become dehydrated includes: (3)
• Inadequate fluid intake
• Excessive sweating
• Failure to replace fluid losses during and after exercise
• Exercising in dry, hot weather
• Drinking only when thirsty
• Exercising at high altitude
• Exercising for long periods (more than 1 hour) without adequate rehydration
Signs that you may be dehydrated
1. Dark coloured urine
2. Dry or sticky mouth
3. Low or no urine output
4. Not producing tears
5. Weakness / reduced skill level
7. Skin may `tent` when pinched (doesn’t bounce back quickly when released).
8. Cramping easily
9. High pulse rate
10. Increased perceived exertion
11. Reduced mental function
12. Stomach upset
How much fluid do you need to keep hydrated?
There are ways to assess exactly how much fluid your body needs to keep hydrated during a workout, performing the sweat rate test will give you your individual fluid need during exercise.
Basic sweat rate testing
You can estimate your fluid requirements by weighing yourself before and after training or games. Each kilogram (kg) of weight lost is equivalent to approximately one litre (L) of fluid. (4)
1. Weigh yourself before training (Initial Weight)
2. Weigh yourself after training (Final Weight)
3. Subtract Final Weight from Initial Weight.
4. The difference plus the volume of fluid consumed during training gives you your sweat rate for that period of time.
5. Divide this by the total time (hours) to determine hourly sweat rate.
6. Aim to match fluid intake to sweat rate
Sweat Rate (L/hr) = [Initial Weight (kg) - Final Weight (kg)] Fluid (L)/Time (hrs)
(The above example is courtesy of the Australian Institute of Sport)
If you don’t want to fiddle about with figuring sweat rates and fluids lost, here are some general guidelines to keeping hydrated whilst exercising
Hydration before Exercise
• Drink approximately 500-600ml, 2-3 hours before exercise
• Drink 200-300ml 10-15 minutes before exercise
Hydration during Exercise
• Drink 200-300ml every 10-15 minutes during exercise
• If exercising longer than 90 minutes, drink 200-300ml of a sports drink (with no more than 8 percent carbohydrate) every 15 - 30 minutes.
Hydration after Exercise
• Weigh yourself before and after exercise and replace fluid losses.
• Drink 600-700ml water for every 500g lost.
• Consume a 4:1 ratio of carbohydrate to protein within the 2 hours after exercise to replace glycogen stores
A note on Hyponatremia
Although rare, athletes can drink too much water and suffer from hyponatremia (water intoxication). Drinking excessive amounts of water can cause a low concentration of sodium in the blood - a serious medical emergency. (1)
What fluid should you drink, water or a sports drink?
Water is cheap and effective for hydration in low intensity or short duration workouts (less than one hour). A sports drink is ideal for longer sessions and where sweat losses are high (e.g. when training in hot or humid conditions).
Sports drinks provide carbohydrates to top up fuel levels during exercise and electrolytes such as sodium and potassium which help you retain more fluid and replace the electrolytes lost in sweat.
The lowdown on electrolytes
You can think of electrolytes like you think of oil in a car, they don’t make the engine run but they’re indispensable to keep things running smoothly. (2)
Electrolytes are positively ( ) and negatively (-) balanced charged minerals (ions). These ions dissolve and separate in water enabling it to become electrically conductive. This allows us to carry electrical impulses around the body i.e. messages. (2)
During exercise, electrolytes play a vital role in nerve transmission and muscle contraction. In addition to this, electrolytes assist with maintaining water balance and distribution between cells (osmosis) along with maintaining an optimal pH balance. You can see why having the correct balance of electrolytes is so important. (2,3)
The main electrolytes are magnesium, potassium, sodium, calcium and chloride. Each electrolyte has an individual function that is vital for your body to function correctly. Listed below are some functions of these main electrolytes: (2,3)
Magnesium is essential for energy conversion, muscle function, nerve conduction, over 300 different enzyme reactions, bone and tooth formation, and pH balance.
Potassium is abundant inside the cells and essential for muscle function, nerve conduction, water balance, and pH balance.
Sodium is essential for thirst response, heat tolerance, muscle contraction, nerve conduction, water balance, and pH balance.
Calcium is essential for nerve conduction, muscle contraction, blood clotting, bone and tooth formation, and heart function.
Chloride is the most abundant negatively charged electrolyte in the body and is essential for oxygen exchange, digestion, water balance, and pH balance.
What is the best way to replenish your Electrolytes?
Remember, our diets generally provide more than enough of the electrolytes needed to execute the biological functions that require them. Therefore, we don’t need to be concerned with replenishing electrolytes before an exercise session.
Post-exercise is the most important time to consider electrolyte replenishment, particularly if you’re unable to take in enough fluid during a workout - it’s not always so easy to drink and workout at the same time.
Electrolytes can be replaced by consuming a variety of food or drink choices. Specially made sports drinks (enhanced with electrolytes) are now commonly available and are very useful and convenient.
Despite this, it is essential to be aware that some brands claim to be helpful in replenishing electrolytes, yet they are filled with sugars and additives - adding unnecessary calories and strain to the body.
Drinks that provide approximately 3-10% carbohydrates and 120-170 mg of sodium per 200ml of fluid are best suited for replenishment. (3)
It is always recommended to find a product that provides minimal sugar and a good supply of electrolytes. Products that I recommend are ‘Endura’ rehydration powders and ‘Mag Primer’ made by Balance.
Which foods best replace Electrolytes?
There is a selection of foods that can help to replace lost electrolytes after a hard or long exercise session.
Here is a list of the best foods you could eat to achieve this, they can be eaten as a snack or included in post workout meals
• Leafy greens
• Coconut Water
• Dried Apricots
• Sea Salt
• Sweet Potato
Homemade Electrolyte Replenishment Drink Ideas
2 bananas, 1 cup blueberries (fresh or frozen), 2 celery stalks, 2 cups water - mix altogether in a blender.
2 bananas, 2 cups water, 2 celery stalk - mix altogether in a blender.
½ fresh orange juice, half water, pinch sea salt.
Or simply 1 cup coconut water with ice.
When it comes to keeping hydrated during exercise its important that you are smart about which climate you train in and ensuring you are getting adequate fluid replenishment whether that be plain old water or an electrolyte drink.
Be aware of the signs of dehydration and if you start to exhibit dehydration signs stop and rehydrate immediately as dehydration can have serious effects. Always rehydrate after a training session and include some foods rich in electrolytes in your post training meal. Staying hydrated is a simple way to ensure you get the most out of your work out.
Written by Lea McIntyre - Naturopath - ND BHSc
Lea has had many years of professional experience as a naturopath working with her patients and clients both in her clinic and as a senior retail naturopathic adviser. When Lea is not helping people stay well and enjoy a healthy lifestyle, she is busy caring for and nurturing her two young children.
1. Consensus Statement of the 1st International Exercise-Associated Hyponatremia Consensus Development Conference, Cape Town, South Africa 2005. Clinical Journal of Sport Medicine. 15(4):208-213, July 2005.
2. ACSM Position Stand, American College Of Sports Medicine, Medicine and Science in Sports and Exercise, 2007. Institute of Medicine. Water. In: Dietary Reference Intakes for Water, Sodium, Chloride, Potassium and Sulfate, Washington, D.C: National Academy Press, pp. 73–185, 2005.
3. J Sports Sci. 1997 Jun;15(3):297-303.Recovery from prolonged exercise: restoration of water and electrolyte balance. Maughan RJ1, Shirreffs SM.
4. J Sports Sci. 1991 Summer;9 Spec No:117-42.Fluid and electrolyte loss and replacement in exercise. Maughan RJ.
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