What’s all the Hype about Hydration?

Fluid and electrolyte balance are the most important factors associated with maintenance of a high level of athletic performance. Effects of dehydration on aerobic endurance occur when hydration levels drop 2% or more of body weight leading to changes in cardiovascular function and problems with body temperature regulation. Gastrointestinal distress is common and functioning of the brain can be impacted, resulting eventually in central fatigue or heat exhaustion.

Hydration

Hydration during exercise and heat stress are among the most studied areas of exercise science, yet many athletes and coaches remain confused over how to advise their athletes to drink under different conditions. For example, is dehydration always dangerous, when are sports drinks better than water, and when should an athlete consider using sports drinks with higher levels of electrolytes? We’ll consider these questions, following review of some basic principles.

It is well known that the sensation of thirst is a poor predictor of hydration, since most athletes only begin to feel thirsty when the body has lost 1.5-2 liters of water. Once thirst is obvious, most people are dehydrated and their performance could be impaired. A good indicator of proper hydration is the ability to produce straw-coloured urine.

One to two hours prior to starting any endurance exercise, it is wise to drink up to 500 ml of fluid. All fluids, count, even that contained within food and those that contain caffeine! (It has been proven that caffeine is NOT dehydrating!) Fifteen to 20 minutes before the start of an activity, drink another 500 ml of fluid. Start your activity with a belly full of fluid!

During exercise, sweat loss typically ranges from 0 – 2 liters per hour, but some athletes can lose up to 4 liters of sweat per hour under identical conditions. Your sweat rate can vary, and is largely determined by

genetic tendency to sweat
fitness status
your body’s acclimatization to environmental conditions like temperature, altitude, relative humidity and wind
exercise duration
exercise intensity
clothing worn.

There are many different opinions from different professional organizations concerning fluid and electrolyte replacement, but they all tend to encourage adequate replacement of any losses from sweat and urine. Some encourage 400-800 ml over this amount. An athlete should be encouraged to estimate his or her own losses over time by weighing in nude before starting (noting time) and after a run once toweled off and having urinated (note time again). Subtract the finishing weight and weight of fluids consumed from the starting weight. (Allowing 1 liter or 1000 ml of water weighs 1 kg or 2.2 pounds). Extrapolate the sweat rate per hour.

Here are some tips to consider during exercise:

Take fluid with you. Wear a bottle belt or fluid pack.
Aim to drink enough to replace both fluid and electrolyte losses.
Research has shown that athletes tend to drink more adequate amounts of sports beverages as compared to water
Know the warning signs of dehydration: (unusual fatigue, lightheadedness, headache, dark urine, dry mouth.)
Drink early and often, but do not over-drink
Keep a comfortably full stomach during the activity.
One medium mouthful of fluid = 1 ounce or 30 ml.
Practice drinking during training
Stop to drink if necessary – you will more than make up the difference.
Have a variety of beverage flavours to choose from.
Drink by schedule, not by thirst.
Grab 2 cups of fluid at each station.
Put more fluid in your belly than over your head. Pouring water over your head does nothing to lower your body temperature.

Electrolytes and Problems Related to Fluid and Electrolyte Imbalance

Electrolytes (sodium, chloride, potassium, magnesium and calcium) are lost in urine and sweat. Under normal, non-exercising conditions, these losses tend to be small. However, when exercising, sodium in particular tends to reach a deficit level ranging from 20-100+ mmol/litre sweat lost. This must be replaced to avoid heat-related problems such as hyponatremia, heat cramps and heat exhaustion or heat stroke.

Heat cramps are painful spasms in the legs and abdomen. Heat cramps tend to occur late in the day after the consumption of large volumes of plain water. Increasing salt intake helps to correct or prevent severe whole-body muscle cramping that seems to result from chronic sodium deficits. Some people mistakenly believe that potassium loss is the culprit, but research has shown that the concentration of potassium in sweat is usually less than 10 mmol/Litre, much less than sodium.

At the first sign of involuntary muscle spasms, consume 500 ml of a sports drink (Gatorade, Powerade or Allsport) supplemented with 1 tsp table salt, or a sports drink which itself contains more sodium (eLoad). Follow with a steady intake of sodium-supplemented sports drinks or nibble on salty snacks with your sports drink for the remainder of the session.

Cramp-prone athletes may ordinarily consume relative low levels of sodium in their diets, may tend to sweat profusely at the beginning of their exercise, and leave a visible, chalky accumulation of salt on their clothing. They may have had poor hydration habits in the past. Gradual inclusion of some more “salty” foods or snacks can also help guard against repeated bouts of cramping.

Heat Exhaustion or Heat Stroke: The symptoms of heat stroke include cold, clammy skin, weakness, faintness, fatigue, nausea and a weak pulse. If severe, sweating no longer occurs and the skin may feel dry. The sufferer is likely to collapse to the ground in a semi-conscious state. Symptoms usually respond well to cooling, so individuals should be cooled quickly with whatever means are available (cool wash cloths applied to the face and body, and even immersion in a cold-water bath). If conscious, sips of cold liquids could be offered, but not forced, as this can cause nausea. Under no circumstances should the person continue to exercise, as this can cause a rapid and dangerous rise in core temperature. Instead, rest is the best medicine, along with drinking sports drinks to assist re-hydration.

Hyponatremia: Drinking only water or very dilute drinks while exercising for a long period of time can lead to hyponatremia or very low levels of sodium in the bloodstream. This can cause rapid swelling of the brain, a potentially fatal condition. Symptoms include headache, confusion, nausea, cramping, swollen ankles and fingers, bloated stomach, seizures and coma. Low blood sodium is most likely to occur during prolonged exercise in dehydrated athletes who sweat a lot. It can also occur among people who ordinarily consume a low salt diet. Adding salt to meals, snacks and beverages is a good strategy to reduce this risk.

To summarize, current research points toward following some practical advice:

When performance is at stake, or whenever athletes want to get the most out of their bodies during exercise, it is always better to be well-hydrated than dehydrated.
To maintain cardiovascular and thermoregulatory function during exercise, fluid intake should approximate sweat rate. Take the time to determine how much you need under a variety of conditions.
When sweat loss is low (eg: less than 1 L/hour) and performance is not a concern, it is fine to wait after exercise to re-hydrate
Dehydration during exercise is far more common than hyponatremia, so drink!
In terms of performance, a well-formulated sports drink is always superior to water.
A no-calorie sports drink is an oxymoron. Sports drinks should be formulated to replace the water, sugar, and salt that is lost during exercise.

References:
Murray, Bob. Fluid, electrolytes and exercise. Sports Nutrition: A Practice Manual for Professionals, 4th edition. Am Diet Assoc 2006

Benardot, D. Fluids and electrolytes. Advanced Sports Nutrition. Human Kinetics, 2006

Murray, Bob. Hydration science-from hype to hyponatremia. SCAN’s Pulse 28:3:17. Am Diet Assoc 2009

	What’s all the Hype about Hydration? Fluid and electrolyte balance are the most important factors associated with maintenance of a high level of athletic performance. Effects of dehydration on aerobic endurance occur when hydration levels drop 2% or more of body weight leading to changes in cardiovascular function and problems with body temperature regulation. Gastrointestinal distress is common and functioning of the brain can be impacted, resulting eventually in central fatigue or heat exhaustion. Hydration Hydration during exercise and heat stress are among the most studied areas of exercise science, yet many athletes and coaches remain confused over how to advise their athletes to drink under different conditions. For example, is dehydration always dangerous, when are sports drinks better than water, and when should an athlete consider using sports drinks with higher levels of electrolytes? We’ll consider these questions, following review of some basic principles. It is well known that the sensation of thirst is a poor predictor of hydration, since most athletes only begin to feel thirsty when the body has lost 1.5-2 liters of water. Once thirst is obvious, most people are dehydrated and their performance could be impaired. A good indicator of proper hydration is the ability to produce straw-coloured urine. One to two hours prior to starting any endurance exercise, it is wise to drink up to 500 ml of fluid. All fluids, count, even that contained within food and those that contain caffeine! (It has been proven that caffeine is NOT dehydrating!) Fifteen to 20 minutes before the start of an activity, drink another 500 ml of fluid. Start your activity with a belly full of fluid! During exercise, sweat loss typically ranges from 0 – 2 liters per hour, but some athletes can lose up to 4 liters of sweat per hour under identical conditions. Your sweat rate can vary, and is largely determined by genetic tendency to sweat fitness status your body’s acclimatization to environmental conditions like temperature, altitude, relative humidity and wind exercise duration exercise intensity clothing worn. There are many different opinions from different professional organizations concerning fluid and electrolyte replacement, but they all tend to encourage adequate replacement of any losses from sweat and urine. Some encourage 400-800 ml over this amount. An athlete should be encouraged to estimate his or her own losses over time by weighing in nude before starting (noting time) and after a run once toweled off and having urinated (note time again). Subtract the finishing weight and weight of fluids consumed from the starting weight. (Allowing 1 liter or 1000 ml of water weighs 1 kg or 2.2 pounds). Extrapolate the sweat rate per hour. Here are some tips to consider during exercise: Take fluid with you. Wear a bottle belt or fluid pack. Aim to drink enough to replace both fluid and electrolyte losses. Research has shown that athletes tend to drink more adequate amounts of sports beverages as compared to water Know the warning signs of dehydration: (unusual fatigue, lightheadedness, headache, dark urine, dry mouth.) Drink early and often, but do not over-drink Keep a comfortably full stomach during the activity. One medium mouthful of fluid = 1 ounce or 30 ml. Practice drinking during training Stop to drink if necessary – you will more than make up the difference. Have a variety of beverage flavours to choose from. Drink by schedule, not by thirst. Grab 2 cups of fluid at each station. Put more fluid in your belly than over your head. Pouring water over your head does nothing to lower your body temperature. Electrolytes and Problems Related to Fluid and Electrolyte Imbalance Electrolytes (sodium, chloride, potassium, magnesium and calcium) are lost in urine and sweat. Under normal, non-exercising conditions, these losses tend to be small. However, when exercising, sodium in particular tends to reach a deficit level ranging from 20-100+ mmol/litre sweat lost. This must be replaced to avoid heat-related problems such as hyponatremia, heat cramps and heat exhaustion or heat stroke. Heat cramps are painful spasms in the legs and abdomen. Heat cramps tend to occur late in the day after the consumption of large volumes of plain water. Increasing salt intake helps to correct or prevent severe whole-body muscle cramping that seems to result from chronic sodium deficits. Some people mistakenly believe that potassium loss is the culprit, but research has shown that the concentration of potassium in sweat is usually less than 10 mmol/Litre, much less than sodium. At the first sign of involuntary muscle spasms, consume 500 ml of a sports drink (Gatorade, Powerade or Allsport) supplemented with 1 tsp table salt, or a sports drink which itself contains more sodium (eLoad). Follow with a steady intake of sodium-supplemented sports drinks or nibble on salty snacks with your sports drink for the remainder of the session. Cramp-prone athletes may ordinarily consume relative low levels of sodium in their diets, may tend to sweat profusely at the beginning of their exercise, and leave a visible, chalky accumulation of salt on their clothing. They may have had poor hydration habits in the past. Gradual inclusion of some more “salty” foods or snacks can also help guard against repeated bouts of cramping. Heat Exhaustion or Heat Stroke: The symptoms of heat stroke include cold, clammy skin, weakness, faintness, fatigue, nausea and a weak pulse. If severe, sweating no longer occurs and the skin may feel dry. The sufferer is likely to collapse to the ground in a semi-conscious state. Symptoms usually respond well to cooling, so individuals should be cooled quickly with whatever means are available (cool wash cloths applied to the face and body, and even immersion in a cold-water bath). If conscious, sips of cold liquids could be offered, but not forced, as this can cause nausea. Under no circumstances should the person continue to exercise, as this can cause a rapid and dangerous rise in core temperature. Instead, rest is the best medicine, along with drinking sports drinks to assist re-hydration. Hyponatremia: Drinking only water or very dilute drinks while exercising for a long period of time can lead to hyponatremia or very low levels of sodium in the bloodstream. This can cause rapid swelling of the brain, a potentially fatal condition. Symptoms include headache, confusion, nausea, cramping, swollen ankles and fingers, bloated stomach, seizures and coma. Low blood sodium is most likely to occur during prolonged exercise in dehydrated athletes who sweat a lot. It can also occur among people who ordinarily consume a low salt diet. Adding salt to meals, snacks and beverages is a good strategy to reduce this risk. To summarize, current research points toward following some practical advice: When performance is at stake, or whenever athletes want to get the most out of their bodies during exercise, it is always better to be well-hydrated than dehydrated. To maintain cardiovascular and thermoregulatory function during exercise, fluid intake should approximate sweat rate. Take the time to determine how much you need under a variety of conditions. When sweat loss is low (eg: less than 1 L/hour) and performance is not a concern, it is fine to wait after exercise to re-hydrate Dehydration during exercise is far more common than hyponatremia, so drink! In terms of performance, a well-formulated sports drink is always superior to water. A no-calorie sports drink is an oxymoron. Sports drinks should be formulated to replace the water, sugar, and salt that is lost during exercise. References: Murray, Bob. Fluid, electrolytes and exercise. Sports Nutrition: A Practice Manual for Professionals, 4th edition. Am Diet Assoc 2006 Benardot, D. Fluids and electrolytes. Advanced Sports Nutrition. Human Kinetics, 2006 Murray, Bob. Hydration science-from hype to hyponatremia. SCAN’s Pulse 28:3:17. Am Diet Assoc 2009