Sunday, March 6, 2011

Electroyte, Fluid and Carbohydrate Replacement During Exercise

Fluid replacement requires more than just water for ultra distance events 

This is a tough area of training/racing to get right as there are so many variables such as environmental conditions, exercise intensity and pre-training/event fluid/nutritional name but a few.  I, like so many others have struggled gastrointestinally and performance-wise when the combination of fluid, electrolyte and carbohydrate intake has been off balance.............just ask my poor training partner Andy!  There is a process of trial and error to getting things correct as we each have an individual response but keeping the exercise science principles and research in mind is also important. 

Here are some principles to keep in mind......... distance events require adequate fluid, electrolyte and carbohydrate replacement and not always in that order at every stage of the event or training. 
  • The stomach can only empty approximately 300-600ml fluid per hour under exercise conditions, however gastric emptying can be accelerated by ensuring isotonic solutions are cold (7-15deg) with more than 200ml being ingested at the one time.  Volumes less than this tend to 'slosh' around and not clear and can lead to sensations of nausea. 
    See full size image
    Endura has correct levels
    of electrolyte replacments and
    is used during TNF100event
  • Especially so for ultras, electrolyte intake needs to include 60mmolL-1 sodium, 60mmolL-1 chloride and 1.5mmolL-1 magnesium and 1.5mmolL-1 potassium per litre of water.  Hyponatremia is a real certainty if these essentials are not replaced on an hour by hour basis. 

  • If ingesting carbohydrates in the form of fluid or in conjunction with electrolytes, then the concentration should not exceed 5-10%.  There will be issues of absorption if fluid forms of CHO are greater than this; the fluid ingested then becomes hypertonic...essentially drawing cellular and circulation fluids into the gut due to the greater concentration gradient.  Remember also that the body can only process about 200-300calories per hr under exercise conditions.  Put more in than this and gastroinestinal issues will result. 
  • CHO intake should come from a variety of sources and should include glucose, fructose and maltodextrins.  Frustose is preferentially delivered to the liver so that liver glycogen stores are topped up ahead of muscle requirements. Remember that once muscle glycogen stores are depleted, the liver stores of glycogen are your backup energy supply.  Have minimal liver glycogen available in addition to minimal muscle glycogen and you are in real trouble.
  • You won't get the electrolyte requirements for an ultra event from the food you eat, so you will most certainly need to supplement with electrolyte fluids or tablets/capsules and this will need to be done during the legs and not just at check points due to the length of time it can take to get to the checkpoint in events such as The North Face 100. 
  • Vegemite and white bread is a popular combination

  • It is important to get your CHO intake from forms of solid food and not just gels.  Liquid forms of gels over lengthy times have been associated with blockage of the glomerular filtration units within the kidney and have resulted in kidney failure, with some athletes requiring dialysis.  The key here is to eat solid food combined with gels (if you must) and adequate fluids. 
    See full size image
    Fruitbuns are also
    a good option on race day
  • An understanding of the different types of fatigue are important also…ie: dizziness…blood glucose needs addressing, wobbly legs….muscle/liver glycogen needs addressing; central fatigue….slowing down/stopping, and all of the above!  As soon as you can’t do mental maths calculation when you could earlier is a sign that you need to address blood glucose or ensure adequate fluid/electrolyte replacement in conjunction with your CHO intake.  This is sometimes easier said than done!
There is a lot of information available, but always ensure that what you read/hear/seek relates to ultra distance events as requirements for shorter events vary considerably.  If you implement principles that apply to half marathons for example in your preparation for an ultra, this could see you not onlt DNF but also compromise your short term and long term health.  One of the bibles for runners is ‘The Lore of Running’ by Dr Tim Noakes….medical doctor, physiologist and endurance athlete.  This is a must for anyone keen to learn more about all aspects of running.  Scientific journals such as the Journal of Physiology are also a good read. Trial and error will inevitably form a part of what we all do, but ensure that this is done on a basis of accurate and evidenced based information and not just hearsay.  There is too much as risk otherwise. 
Happy running and looking forward to May 14!