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The Importance Of Hydration

Avatar for Hadyn Luke Hadyn Luke posted this on Friday 12th of April 2013 Hadyn Luke 12/04/2013


The Importance Of Hydration


We all know we should drink plenty of water, especially when exercising – in this blog we look at why this is considered important.

Hydration is essential for optimal health. Research has shown that maintaining the correct balance of fluids and electrolytes in the body can reduce the risk of some diseases and infections, kidney stones and possibly even cancer.


The Department of Health recommends that we drink 1.2 litres of water a day. This is best consumed in steady amounts throughout the day, for example, six 200ml glasses or eight 150ml glasses at regular intervals. 

People who lead sedentary lifestyles – driving rather than walking and sitting at a desk all day – will need less hydration than those who are active, as they won’t be losing as much water through perspiration.

Most clients that a personal trainer or fitness professional come into contact with, however, will be physically active – whether running, cycling, playing sport, using gym equipment or following activity classes – and will therefore need additional hydration above the standard recommended 1.2 litres. The more we exercise, the more we will perspire, especially in a warm environment.


On average, an hour of vigorous exercise will result in 500-1,500ml of water loss. This can fluctuate depending on the individual, on the type and intensity of the exercise and on outside influences such as the type of clothing worn and the ambient room temperature or outdoor temperature if running or playing sport outside.

A personal trainer may want to advise a client to get on the scales before and after exercise to see how much water they have lost and therefore how much they will need to rehydrate. The fitness instructor should also explain to the client that any weight loss measured immediately after a workout is from sweating, not burning fat.


Personal trainers may find that some clients say that they never drink during exercise and yet claim to feel absolutely fine. However, they should be advised that once they are sweating at a certain level, it will inevitably result in dehydration if they don’t replace lost fluids.

An article by Beth Stover and Bob Murray (“The Science of Hydration”, ACSM Health and Fitness Journal, March/April 2007) points out that loss of water through sweat of more than 500ml can have negative physiological consequences. These include:

  • a reduction of blood volume
  • more viscous blood
  • increased heart rate
  • difficulties in losing heat from the body


When exercising, as opposed to when sedentary, it’s harder to get an accurate idea of dehydration based on thirst alone. Yet even a 2% decrease in total body water can affect concentration and performance as well as causing headaches and lethargy.

A personal trainer may find that a client is struggling to complete an exercise or stops a gym session early because they feel that their energy is low, when in fact they are simply dehydrated.

Although rehydration after exercise is better than no rehydration, it’s better to replace any fluid loss during exercise, in order to maintain the intensity of the workout and keep a higher concentration of water in the muscles – this makes them less likely to fatigue.

As the authors of the article explain: “proper hydration during exercise enables people to work harder and longer, helping them get the most out of each workout”.


In many cases, plain water is sufficient to replace fluid lost through sweat during exercise. Lightly flavoured, low-calorie water can be a good alternative, as it is more likely to stimulate a client’s desire to drink than plain water.

Those undertaking a more intensive workout or training at an elite level and therefore sweating more profusely may benefit from sports drinks. As with flavoured water, these stimulate drinking, but the carbohydrate content in a carefully formulated sports drink will also provide energy to help the working muscles. Sports drinks also contain electrolytes to replace what is lost through sweat and help the body retain the fluid consumed.


If an individual drinks an excessive amount of water very quickly it can lead to hyponatremia. This is a reduction in the concentration of sodium in the blood, which has an impact on the balance of electrolytes.

At low levels this can cause headaches and nausea; taken to extreme, the brain can swell, causing disorientation, seizures, congestion in the lungs and, ultimately, coma and death. Hyponatremia is, however, an extreme condition and much less common than dehydration.

In conclusion, a personal trainer should ask a client to bring water with them to sip during their workout, or a sports drink for a more intensive session. They should also be aware of different client’s hydration needs, depending on the individual and the intensity of their workout.

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