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Dehydration & Energy Factor


The sight of runners walking up from Esk Hause to Scafell in the Wasdale is traditional, but not always necessary.  The reason for walking, apart from injury, is that they have either run short of energy, (muscle glycogen), or they have de-hydrated.

The body is a marvellous machine; the analogy I like to use is the car.  As long as you keep topping it up with fuel and ensure its not short of water, and dont exceed its speed limit, it will serve you well.

One of the most misunderstood aspects of energy expenditure is the volume of fluid that the body uses when working at a high capacity.  The second is the percentage volume of the body thats occupied by fluid.  In young adults the percentage of body weight represented by water will average about 57% for males, and 47% for females.  So if we have an athlete weighing 10st (63.5kg) and rung him out, he would weigh in, (shorts and all) at approximately 4 stone (25kg)!

A simple known fact, is that to lose 2% of body mass, in this case approximately 3lbs (1.36kg) will reduce performance by up to 20%.  When it falls to 4% loss, 6lbs, you will probably be walking and not feeling too well.  Once it falls to 6% (9lbs) you could be in real trouble.

When your body is short of water it correspondingly depletes its electrolyte level.  Homeostasis is affected and all sorts of imbalances go on inside the body.  The cardiovascular system has to work harder to pump blood around the body, which affects your performance.

To understand the principle of drinking what is possibly considered ridiculously large amounts of water, we need to look at what the body can do when the right amount of water, and fuel, are topped up at regular intervals.

A young 0/60 vet from Horwich set off in April 96 to run the Joss Naylor Lakeland Challenge from Pooley Bridge near Ullswater, to Greendale Bridge at Wasdale.  His time limit was 18 hours in which time he had to cover 48 miles and climb 16,500 feet.  In fact he did it in 16 hours 56 mins. The reason this little story is told was that he, along with others, was initially rather sceptical of the excessive amount of water prescribed, along with the energy content of over 4000kcal.

The formula that was used was as follows: He weighed in at around 70kg and we knew the distance to be covered was 77km. Knowing the recognised formula of 1kcal per kg of weight, per km of distance (allowing for all the climbing with extra food and snacks) gives the calculation of 70 x 77 = 5390kcal.  Not wanting him to have all his energy by fluid we settled on 4000kcal with a pure carbohydrate hypertonic drink.

At 80kcal a scoop, 50 scoops were put into 10 litres of water, which he consumed over the 17 hours, much to his surprise.  He did get a little help from the support crew in encouraging this feat, especially as it was less for them to carry.  He duly arrived at Greendale Bridge an hour inside the time, after successfully negotiating some arduous sections, some covered in snow.  His condition at the end was to say the least amazing, he looked fine.

Most runners are unaware that their feeling of fatigue can sometimes be just a case of mild de-hydration.  If you work on the simple rule of at least a pint an hour, with the necessary energy content you wont go far wrong.

Drinking en-route is obviously only necessary if the duration of the race demands it, but hydration before any race, even short, should be a matter of course.  Also be aware of the diuretic influence especially of alcohol taken the night prior to a long run.

The availability of water can be a tactical ploy in any medium or long race, good reconnoitring of the race route is essential, especially if the weather has been particularly dry.

The easiest and quickest way to take water from a stream is to have a plastic bag containing the necessary carbo powder.  Remove it from the bum-bag before the stream is reached; dip it in with the top open.  In this way you can scoop a good measure, which you can drink over the next 100m or so - on the run of course!  The technique is to make a seal by folding back the top of the bag and squeezing it tight.  You then push the forefinger in to the opening on the top of the bag creating a small hole which you seal against your mouth and squeeze the bag to force the water out.

If you find that no water is available over the course or part of it, then good preparation either from pre-reconnoitre planting, or friends en route is essential.  A hot day on Ennerdale after Pillar can be a problem without water.  Although most runners like to eat something substantial on long A races, carbo powder is all that is required - trying to eat a chocolate bar climbing Gable can add minutes to your climb.

Important Information

HEAT EXHAUSTION (38C) This is caused by excessive sweating combined with an inadequate water intake.

Signs & Symptoms
   runner will feel exhausted and may complain of a headache
   salt deficiency may cause cramp especially in the lower limbs
   the face will be pale with a rapid weak pulse and fast shallow breathing.

Management of Heat Exhaustion:
   move the runner to a cool environment
   place them at rest
   give cool drinks in small quantities
   administer a salt tablet or slightly salty drinks

HEAT STROKE (40C) Developed from heat exhaustion.

Signs & Symptoms
   unconsciousness may start suddenly and deepen
   pulse - initially rapid and weak becoming full & bounding
   breathing shallow, becoming rapid , noisy and panting
   headache and dizziness - may develop into confusion and delirium
   muscle cramp and twitching - may develop into convulsions
   colour - initially pallid turning flushed; developing congestion of lips and tongue
   skin - sweating and warm, becoming dry and very hot.

Management of Heat Stroke:
 
  remove as much clothing as possible
   wrap in a wet sheet if available
   fan the runner vigorously
   if cold packs are available, place them under the arms and around the neck
   if the runner becomes unconscious, treat accordingly

SNIPPETS

  • For every rise of 0.5C in body temperature the basal metabolism increases by 7%.  Basal metabolic rate is a measure of the energy output of an individual under standard resting conditions.  This creates heat which is measured in kilo calories (kcal).  Metabolic rate is equal to the number of kcal of heat, per kg of body weight, per hour.  A typical person (70kg) at rest creates approximately 1700 kcal of heat per day.

  • Every litre of sweat which evaporates from the skin leads to a loss of about 580 kcal of heat from the body.  If the skin is kept cool artificially by other means, such as wiping away the sweat or being brought into contact with cold water, then the evaporation factor is reduced.

  • You occasionally hear the expression that an athlete can lose up to 2 litres of fluid an hour which would put a Bob Graham runner on 10 gallon of water.  Common sense must prevail when calculating fluid intake.

  • Isotonic drink is one that has the same concentration of dissolved particles - roughly 5-7g per 100ml - as the fluids in the body.  Usually taken to replace fluid lost, with a few little extras.

  • Hypotonic drink is one which is less concentrated than the body fluid and as such can be absorbed more rapidly if you need to replace fluid quickly.

  • Hypertonic drink is one which is more concentrated than the body fluid, usually carbohydrate based that takes longer to be absorbed, and as such is suitable for energy intake over a period of time.


Norman Matthews 2001-2004
Head Senior Coach
Horwich RMI Harriers