This article has been reproduced by the kind permission of the author Jeff Cole of Injury Scene. He can be contacted through his website www.injuryscene.co.uk or mobile 07855113959.

HYDRATION DEHYDRATION HYPONATREMIA

Drink a glass of water and the body starts to hydrate itself. Loose water from the body without replenishing it and the process of dehydration occurs. Hydrate excessively and hyponatremia may occur. Water, tap or bottled, the human body requires it to function. Without it, death occurs within days as apposed to nourishment, when the body can survive for weeks without food.

HYDRATION

The need to properly hydrate at all times of activity throughout the 4 weather seasons, remains an issue that will influence the quality of effort to that of performance.How many athletes whether competing or training recognise this fact?

Water consumption can be in the form of liquids administered orally or in the food that we digest.Water serves many vital functions to the body. Key basics that an athlete should be aware of are:-

• Water is critical in thermoregulation of core body temperature (this is discussed in more detail later). Without adequate hydration, performance will suffer and in severe cases can lead to serious if not fatal heat injury.
• Water flushes waste and toxins out of the body and its systems. Physiological function reduces as the water that acts as a solvent for nutrients and wastes becomes depleted.
• Water is one of the key ingredients of the lubrication that protects the joints of the body.
• Water is vital for the body to convert carbohydrates into energy. 3 grams of water are required to metabolize 1 gram of carbohydrate properly.

So, how does the body lose water? Based on figures for a sedentary person weighing between 130 to 160 lbs, fluid is lost in the following way.

• 1300-1400ml in urine
• 100-150ml in faeces
• 350-450ml via skin perspiration (sweating)
• 350-400ml from respiration

 Added together, water loss can be between 2.1 litres to 2.45 litres per day.Once exercise is undertaken, water loss via sweating can be 14 times greater.  It is easy to conclude that for the active athlete, sweating is the main source of water loss from the body.

Why do we sweat more when we exercise?

When exercise is undertaken, the body burns molecular fuel, mostly glycogen but also some protein, fat and blood glucose form ingested nutrients.  The breakdown of these energy providers releases heat that gradually builds up and raises the body’s core temperature.However for the body to maintain its physiological function, the core body temperature must be maintained around 37 degrees C.To do this, the body has several mechanisms to dissipate the heat generated.

At rest, when the environmental temperature is below body temperature, core body temperature is maintained by convection of heat to the skin’s surface (blood is diverted to the capillaries near the skins surface). This heat is then radiated to the surrounding environment.

As exercise intensity rises, the lungs work harder to provide the working muscles with more oxygen. On expiration of the waste gasses, heat is also removed (visible on a cold day when a vapour trail is formed, on breathing out, as the warm moist air condenses)

Sweating. The body excretes sweat to the surface of the skin which then evaporates, in the right environmental conditions (high humidity reduces the evaporation process), to produce a cooling effect. In hot conditions, convection and radiation ceases to be effective and the body relies solely on the evaporation of sweat to regulate core temperature. (This is around 35 degrees C or above, when the body starts to absorb heat rather than looses heat).

So how does the evaporation of sweat cool the body?  

Sweat evaporation works on a basic physics fact.  Water evaporation is an endothermic process requiring energy (heat) to change from liquid to gas.Water molecules in the gas phase have more energy than water molecules in the liquid phase.As the water molecules evaporate from the skin, they remove heat energy.  The remaining water molecules have less energy and therefore you feel cooler!!

DEHYDRATION

Dehydration occurs when the body’s water loss through sweat, urine/faeces production and respiration is not matched by the intake of fluid to replenish that lost.

Dehydration is the term used to describe the acute change of fluid stores from that of a steady state condition of normal body water to that being something less than normal body water. If decreased body water stores remain depleted for an extended period then the body is regarded as being in a “state of hypohydration”

How can dehydration affect the active athlete?

Most individuals are comprised of between 55-75% water.  Lean tissue carries between 70-75% water, while fat carries in the range of 20% water. Therefore athletes who tend to have less body fat will be in closer to the 75% range.  Any significant decrease in body water stores will alter the physiological function (as discussed earlier) leading to a drop in athletic performance.

The figures below demonstrate at percentages how performance is affected.   Each percentage is body weight loss by sweating. E.G. if you go out for a run weighing 160 lbs and weigh in 20 miles later at 154 lbs, you have lost almost 4% of your body weight.

Symptoms by percentage body weight water loss.

0%      none, optimal performance.

1%      thirst stimulated, heat regulation altered, performance declines.

2%      further decrease in heat regulation, increased thirst.

3%      worsening performance.

 4%      exercise performance cut by 20-30%.

5%      headache, irritability, “spaced out” feeling, fatigue.

6%       weakness severe loss of thermoregulation.

7%       collapse likely unless exercise stops.

10%     comatose.

11%     death likely.

As can be seen, a 1% to 2% water loss would affect performance with a 4% drop leading to a drastic reduction in performance.  How many persons whether they are athletes or not, hydrate only when they feel thirsty?

Unfortunately there are many factors why an athlete may fail to hydrate before, during and after exercise, leading to dehydration.

• As activity rate increases and intensity reaches high levels (more than 75% V.O. max), the rate at which the body can process fluid in the stomach and intestine and then discharge it into the blood stream decreases.
• In extreme heat conditions, 3 litres of sweat can be produced per hour, with the body only capable of replacing 1 litre per hour.
• As the athlete increases exercise intensity, the time available to focus on hydration will decrease.
• No athlete is the same.  Sweat rates can vary drastically between individuals (body size alone can influence sweat rates).  If limited hydration fluid is available, the individual may not be able to replenish to their required amount.
• The athlete may be in a mild state of dehydration having failed to hydrate prior to training/competition.  Dangerous levels of dehydration are reached more rapidly.
• Multiple training or competition events during the day require hydration between events.  Time factors between events may be inadequate to hydrate fully.
• When fluid is not readily available during training/competition events.
• Missed meal times.  Fluid consumption occurs mainly at meal times with fluid being taken along with food or is present in the food eaten.
• If the athlete dislikes what hydration fluids is available, then voluntary consumption may be reduced.
• Individual tolerance to the amount of fluid required to hydrate can vary.  Some athletes cannot tolerate the amount of fluid required to hydrate and need longer to replenish before the next activity session.
• Illness or medication which may affect the ability to absorb water into the bloodstream or which may cause water loss.

HYPONATREMIA

 Whilst the effects of failing to hydrate have been recognised for a long time, the effects of over hydration are now becoming more recognised.

This is particularly more prevalent at endurance events. (Often more than 4 hours).

Caused by two distinctive factors, hyponatremia is the term given to low blood sodium level concentration(less than 130 mmol/l).

The two factors are:-

• Excessive intake of fluids, in relation to that lost via sweat and urine production, over a period of time, causes the concentration of sodium in the blood to lower.  An adequate sodium balance is required for transmitting nerve impulses and for correct muscle function.
• The intake of low sodium fluids that fail to replace what is lost in sweat during exercise.

PUTTING IT ALL TOGETHER

To remain hydrated, prevent dehydration and avoid hyponatremia, the athlete needs to be educated to:-

• Be aware of the physical symptoms associated with dehydration and hyponatremia.
• Replace fluids in appropriate amounts.
• Learn the differences between the types of hydration fluids available.

How do you recognize dehydration?

It is important to remember that while dehydration is an important factor that contributes to hyperthermia associated with exercise, other factors are also very important. For example, intensity of activity, environmental conditions, fitness levels, degree of heat acclimatization, amount of clothing/equipment, illness, etc. all contribute to the rate of rise in body temperature and athletes should consider these when looking to decrease the risk associated with exercise in warm and hot conditions.

Athletes should be able to recognize the basic signs and symptoms of hypothermia of which dehydration may be a contributing factor..

Irritability, and general discomfort, then headache, weakness, dizziness, cramps, chills, vomiting, nausea, head or neck heat sensations, (e.g. pulsating sensation in the brain), disorientation and decrease in performance. If the symptoms are mild, then the athlete needs to slow down or stop. If the symptoms are more severe, an immediate effort must to made to reduce core body temperature

The sensation of thirst is a general indicator of dehydration. It is a clear signal to drink. If the signal of thirst is not used for rehydration, there is greater danger of dehydration and heat illness.

Symptoms that complicate the diagnosis are the feeling of dizziness, weakness and collapsing. When this happens at a point when the athlete has stopped, either along the course or at the finish line, rather than while in motion, the likely cause is postural hypotension which is a pooling of blood in the legs and inadequate blood supply to the upper body. This can be avoided by walking or flexing the legs when standing once exercise has stopped. When a runner collapses from postural hypotension, the legs should be raised above the head and held there for 3-4 minutes. That should relieve the symptoms.

How do you treat dehydration?

>A conscious, coherent, dehydrated athlete without gastrointestinal distress can be aggressively rehydrated orally, whilst a conscious/semi-conscious athlete that is incoherent or has gastrointestinal distress should be examined by trained medical personnel. (Intravenous rehydration is likely to be needed).

How do you recognize Hyponatremia?

Unfortunately, hyponatremia may mimic many of the signs and symptoms of exertional heat stroke, such as nausea, vomiting, extreme fatigue, respiratory distress, dizziness, confusion, disorientation, coma and seizures.

Other symptoms may include:

• • A progressively worsening headache.
• • Normal exercise core temperature
• • Swelling of the hands and feet (which may be noted with tight wedding bands, watches, shoes, etc.).

How do you treat Hyponatremia?

Urgent medical treatment is required and must be sought.

How do you prevent Hyponatremia?

 The most important aspect of preventing hyponatremia lies in having an appropriate hydration protocol for the event or task being performed. A few key points include:

Education regarding replacing fluids in appropriate amounts, not to exceed sweat rates.

Assuring easy access to sports drinks containing an adequate amount of sodium.

Monitoring body weights when feasible to identify those who have gained weight from over drinking.

Additional steps to consider:

Encourage athletes to be well-acclimatized to the heat because this is an effective way to decrease sweat sodium losses.

Maintain normal meal patterns and don’t restrict dietary sodium intake, so sodium levels are normal prior to the start of an event.

Consume a little extra sodium with meals and snacks during continuous days of exercise in hot weather to help maintain blood sodium levels.

How do you prevent dehydration without over hydrating?

Optimum hydration is geared around the general rule that fluid intake should match fluid losses. These processes are extremely individualized. It is an individual process because rehydration practices vary based on a wide-variety of issues (discussed earlier). The crux of this process is trying, to the best of the athlete’s ability, to match fluid intake with fluid losses. If this can be done relatively closely, then all of the hazards of under or over hydrating are avoided. The following guidelines (which are taken from the United States of America Track and Field self testing program for Optimum Hydration) should assist in establishing a hydration protocol:

To correctly assess rehydration needs for individuals, it is of great importance to calculate the individual’s sweat rate.

Calculating sweat rate:-

(Sweat Rate = body weight pre-run – body weight post-run + fluid intake – urine volume/exercise time in hours) for a representative range of environmental conditions, training sessions and competitions.

When establishing an individual sweat rate that will be applicable during a long race, the athlete should try to run at race intensity (for races of 1 hour or more) in a 1-hour training session. Try to establish a sweat rate in similar climatic conditions expected for a targeted race or for long training runs leading up to the race, whichever are in a higher temperature.

Follow this procedure:

The athletes should warm-up to the point where perspiration is generated and then urinate if necessary.

Weigh the athlete naked on an accurate scale. (Calculation A)

The athlete should run for one hour at intensity similar to the targeted race.

Drink a measured amount of a beverage of the athlete’s choice during the run. (Measured in litres, calculation D)

The athlete should not urinate during the run (unless they choose to measure the amount of urine).

The athlete should then be re weighed naked again on the same scale after the run. (Calculation B)

The athlete should then urinate and measure the volume. (Calculation E)

 Calculate the following.

 A-B = C

C+D - E = F

F / time run in mins = sweat loss per min. (G)

G x 60(mins)            = sweat loss per hour

You now know the athlete’s approximate fluid needs per hour for those conditions tested in. A training log indicating conditions such as temperature, humidity, wind and terrain etc will be a useful reference for hydration requirements when training or competing in similar circumstances. The calculations should be performed under a range of these conditions.

 Example.

61.7kg (A) – 60.3kg (B) = 1400g (C)

 1400g + 420ml – 90ml = 1730ml (F)

 1730 / 60 mins running = 28.83ml/min

 28.82 X 60 = 1729.2 ml/h.     If this amount of fluid is taken per hour, hydration needs would be appropriate without being excessive.

 It should be noted that metabolism of carbohydrates, fats, and protein during exercise accounts for a very small amount of the weight lost during activity. The effect of fuel oxidation on weight loss during high sweat efforts is a small enough amount that weight changes that occur following an activity can largely be attributed to sweat losses. Heat acclimatization induces physiologic changes that may alter individual fluid replacement considerations.

First, sweat rate generally increases after 10 to 14 days of heat exposure, requiring a greater fluid intake for a similar bout of exercise. An athlete’s sweat rate should be reassessed after acclimatization.

Second, moving from a cool environment to a warm environment increases the overall sweat rate for a bout of exercise. Athletes must closely monitor hydration status for the first week of exercise in a warm environment.

Third, increased sodium intake may be warranted during the first 3 to 5 days of heat exposure, since the increased thermal strain and associated increased sweat rate increase the sodium lost in sweat.

Adequate sodium intake optimizes fluid palatability and absorption during the first few days and may decrease exercise-associated muscle cramping. After 5 to 10 days, sweat sodium concentration decreases, but the overall sweat rate is higher so the athlete should still be cognizant of sodium ingestion.

Pre-Event Hydration

Runners should begin all exercise sessions well hydrated.

Hydration Status (general guidelines)

 % Body Weight Change = Pre Body Weight – Post Body Weight    X  100

                                                           Pre Body Weight

% Body Weight Change

Well-Hydrated    +1 to -1 % 1 or 2

Minimal Dehydration -1 to -3 % 3 or 4

Significant Dehydration -3 to -5 % 5 or 6

Serious Dehydration > 5 % > 6

To ensure proper pre-exercise hydration, the athlete should consume approximately 500 to 600 ml of water or a sports drink, 2 to 3 hours before exercise and 300 to 360 ml of water or sports drink 0 to 10 minutes before exercise.

Post-Event Hydration

Post-exercise hydration should aim to correct any fluid loss accumulated during the practice or event. Ideally completed within 2 hours, rehydration should contain water to restore hydration status, carbohydrates to replenish glycogen stores, and electrolytes to speed rehydration. The primary goal is the immediate return of physiologic function (especially if an exercise bout will follow). When rehydration must be rapid, the athlete should compensate for obligatory urine losses incurred during the rehydration process and drink about 25% more than sweat losses to assure optimal hydration 4 to 6 hours after the event.

Fluid temperature influences the amount consumed. While individual differences exist, a cool beverage of 10o to 15oC (50o to 59oF) is recommended.

What’s the difference between isotonic, hypotonic and hypertonic fluids?

Isotonic sports drinks

Isotonic drinks have a fluid concentration similar to that of the blood. Therefore it is quickly absorbed into the blood stream, helping to prevent dehydration and also providing energy in the form of simple sugars. It can take up to 10 mins for an isotonic drink to work through your system to the skin, as sweat. It is advisable to start drinking 10 mins before you need the carbohydrate and fluid boost when using this type of drink. Fruit juice diluted ½ and ½ with water (500ml of each) or squash diluted 1:4 (200ml) with water (800ml) with 0.5grams of salt added to either drink.

Hypotonic sports drinks.

Hypotonic drinks have a concentration that is lower than the blood. Therefore these drinks are rapidly absorbed into the blood stream. Water is hypotonic. Fruit juice diluted 1:3 or squash diluted 1:8 parts water.

Hypertonic sports drinks

Hypertonic drinks have a higher concentration than the blood. This slows down the rate at which the stomach empties and therefore reduces the rate of hydration. Generally these are drinks with a carbohydrate content of greater than 8%. These are generally soft drinks that are just marketed at the sports market. Due to the water movement effect that these drinks have it is generally un-advisable for the regular exerciser to use them.

Salt in sports drinks

Sports drinks generally contain an amount of salt. This is useful as it helps replace salts lost in the form of sweat, and also acts to aid fluid absorption in the small intestine. Replacing salt is also important after a work out, if you have not fully replaced your salt stores you will find it more difficult to full re-hydrate.

There is a great performance benefit associated with proper hydration during exercise, but over drinking must be avoided. Athletes who lose and replace fluids at equal rates greatly diminish the risk of hyponatremia, especially if they drink fluids that contain adequate sodium.

This article was written by Jeff Cole of 23k Sports Injury Therapy for the Sports Therapy Organisation’s Journal, 2007.

Sources

Proper Hydration for Distance Running. Identifying Individual Fluid Needs, by Douglas J. Casa, PhD, ATC, FACSM

Noakes, T., Martin, D.E. IMMDA-AIMS Advisory statement on guidelines for fluid replacement during marathon running. New Studies in Athletics 17 (1): 15-24, 2002.

Runners World-Complete Guide to Hydration

Anita Bean- Complete guide to Sports Nutrition

United States of America Field and Track Information services