Are you getting enough fluids?
Mark Fardon explains the facts, fiction and provides some practical advice on fluid intake.
An adult human is made up of 55 to 65% water, which is equivalent to about 9 gallons (40 litres) and is vital to sustain life and is a key ingredient in all body cells and fluids. We can last a lot longer without food (up to 80 days) than water (3 to14 days). Part of the reason for this is that we can store substantial energy reserves as fat, which has a high ratio of energy to its volume, but water cannot be compressed. Unfortunately, fat is not easy to convert to energy for the sort of levels of "fuel" consumption required by an athlete. This is why we use carbohydrate-based diets.
For any sort of power output, we need to transport "fuel" (glycogen) from its "tank" (liver) to the "engine" (muscles). Fluid is the most efficient way of transporting this "potential power". In the case of a car, it is the oil that lets the bearings run smoothly, for us it is blood. If you think of oil in a car, it becomes less efficient as it gets old, petrol gets used up and needs replenishing and you need water in your radiator to stop the engine overheating and seizing. In all these cases the key to the best and most efficient performance is to keep the fluids fresh and topped up!
So how much do we need and what grade should it be?
Like cars, humans are not all the same. Look at us! We get everything from clapped-out bangers, which would not pass an MOT, to high-performance dragsters that go like rockets, but would struggle with a 3-point turn. In between there are family cars, off-roaders, container trucks, motorcycles and a mass of others; but all have one thing in common - they need the right fluids to run and we are the same.
So, effectively water is a catalyst that lets us work properly:
On this basis, it is vital we maintain our levels of fluid when stressing the "engine" (body) in a sport.
How much water do we use in a day?
It depends who we are, what we are doing and where. An average, an inactive individual of 75kg (about 12stone) in a mild climate will use about 2½ litres of water a day (see table below); that is half-a-gallon.
How much do we need to be drinking?
The answer is to always make sure it is enough. Fluid loss is a great short-term way of appearing to lose weight, but it is only temporary and can have serious effects on athletic performance. Just 2% loss will affect your performance and a 5% loss could lead to as much as 30% loss of power output. That may sound like quite a lot. For our 75kg individual, it would mean 4 kgs of water, but if they were 2% below optimum to start, then the loss of just over 2kg will have them hitting the 95% barrier. On a hot day on a bike, this can happen very quickly due to sweat loss.
The thought of having to drink half-a-gallon of water each day while you are at rest may seem a bit daunting - it is. This figure includes the water content of foods, which can be quite substantial. For instance, on a "per edible portion" basis (i.e. not per 100g), tomatoes can have a water content of 93g and white fish 82g, while crisps have just 2g. However dried dates, which are a good energy source, have 12g water but potatoes (another good source of complex carbohydrate, through starch) have 79g water per portion. The solution is to take an interest in what you eat and drink. When you exercise you will lose a lot of weight simply through the fluid losses detailed above. However, there is also a bit of weight lost by using up energy in the form of glycogen that is formed from fat, protein and carbohydrate intake.
But how much do we lose?
As an example, a 10-mile cycling time-trial will use about 500 Calories, which constitutes about 65grams (2.3oz). If you lose more than that - you are dehydrating.
Regulation of body water balance
The following table is a recommended daily intake of water for a sedentary individual with a body mass of 70 to 75kg living in a temperate climate. (Intake = food + drinks + metabolism)
The water content of food - per edible portion
Why do we sweat?
Exercising muscles produce heat, but the body's temperature needs to keep within safe limits, around 37 to 38° C. In order to do this, we work in a similar way to a car's engine, we use a radiator for water-cooling. Sweating is the major way of getting rid of heat from the body (by evaporation). Unlike a car's system, which is sealed and so re-circulates cooled water, ours allows the fluid to evaporate and so needs regular topping up to maintain performance.
The rate of sweating depends on several factors:
How dehydration can affect performance
It is really important to know how well hydrated you are as well as weight and body-fat percentages. This used to be quite expensive and complicated to find out but can now be done with scales that are widely available for less than £100. If that is still too expensive, it may be worth considering buying a set as a group (a sports club). The only caveat would be to make sure they are cleaned properly between users to avoid risks of passing foot problems such as verrucas between users. The scales work by passing a small pulse between the feet and measuring the resistance, compared with the user's age, height and sex.
Accuracy is normally pretty good and permits a graphic record of improvements in weight, fat and hydration management.
What actually happens?
To sum up - monitor yourself
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About the Author
Mark Fardon is a UK Cycling Coach and works in the IT sector. He gained his first coaching qualification in 1981 from BAWLA (British Amateur Weightlifting Association) and went on to gain cycling-specific coaching qualifications with the Association of British Cycling Coaches and British Cycling Federation. The riders Mark coach have ranged from 12 to 84 years and have ranged from world-class triathletes and mountain-bikers to complete novices, aiming simply to get fitter and lose weight.
The following Sports Coach pages provide additional information on this topic: