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When out on your bike have you noticed any of the following symptoms towards the end of a ride?:


  • increased heart rate
  • increased breathing rate
  • increased body temperature
  • fatigue
  • muscle cramps
  • headache
  • nausea


I would be most surprised if you haven’t.  Most of us put this little list of common cycling ailments down simply to not being as fit as we should be.  Whilst this is probably true and will not help the situation, it is much more likely that the main cause of all or any of these symptoms is dehydration.


Your body is over 70% water.  So you can imagine that it is quite important stuff.  Unfortunately the body uses it up and leaks it out so we have to drink to top our supplies up.


There is a lot of scientific research about what happens when we become dehydrated; which are the first parts of the body to dry up and die etc..  All pretty gruesome reading.  But, without getting into the whys and wherefores, the consequences of not keeping your water tanks full (becoming dehydrated) are generally agreed as the list above.  The amount you have to become dehydrated to experience these symptoms varies from research to research but you should start to suffer from them if you are 3-5% dehydrated.  This means your water tanks are 3-5% empty.


However, research has also shown that the body’s ability to produce energy can be significantly affected by even a small drop in hydration and that this increases with each further percentage drop.  When you bear in mind other research that suggests we generally operate at 1% dehydrated this means that normally we are under performing from the moment we get on our bikes.  Then as the ride progresses, if we put in less liquid than we leak out, our ability to produce energy gets worse and our performance suffers.  If we let our water tanks deplete to the 3-5% level we being to suffer the more severe symptoms listed above.


If you become 10% dehydrated you can expect:


  • muscle spasms
  • vomiting
  • racing pulse
  • shriveled skin
  • dim vision
  • painful urination
  • confusion
  • difficult breathing
  • chest and abdominal pain
  • seizures
  • unconsciousness


Of course if you are grinding up a 20% climb you might well have a racing pulse and difficulty breathing and arguably you must have been pretty confused to go that way in the first place.  And the two bottles of red wine (lots of antioxidants) you got through last night might account for the shriveled skin, dim vision and vomiting.  So just because you have some of these symptoms doesn’t necessarily mean you need hospitalization.  Just be aware.  Especially if you consider that if you become more than 10% dehydrated you might die.


Now, that is all very good, but you do not actually have water tanks with handy gauges to tell you how full of water you are, so how can you tell?  The most obvious indicator the body has for dehydration is thirst.  Unfortunately the consensus of scientific opinion seems to be that you are already 2-3% dehydrated before you feel thirsty.  So if you wait until you are thirsty you are already substantially underperforming and getting close to the first list of symptoms.


Another indicator is the colour of your wee.  When fully hydrated it should be the colour of pale straw (nice subjective term for you to argue over with your riding companions – “Does this look like pale straw to you?”).  The point is, your body starts to regulate water when the level in the tanks starts to go down.  Less is leaked out in your urine so it becomes darker in colour.  If you notice it becoming darker during a ride you need to start drinking more. 


It is always best to know your own body and to have some idea of how dehydrated you are getting whilst riding over various distances.  To judge your hydration levels weigh yourself before and immediately after a ride.  Any weight you have lost in kilos is equivalent to fluid loss in litres (roughly 1lb loss = 1 pint).  So if you have lost 2 kg you have used up 2 litres from your tanks.  This needs to be replaced at 1½ x the fluid loss so you will need to drink 3 litres of water to fill your tanks.  And also means you should have drunk this much more on your ride.  If you have gained weight during your ride you should consider spending less time on the pub break next time.


Also take into consideration the temperature and riding conditions.  You will need to drink much more in hot sunny conditions than in cold wet ones.  And a flat route will probably result in less liquids leaking out of you than a hilly one.


Most of your fluid loss will be due to sweat.  This means that your body will be losing vital salts as well.  Make sure that these are replaced.  The easiest way to do this is with isotonic drinks and gels or with isotonic tablets added to your water bottles.


So the answer is to know your body and drink, preferably little and often.  And if you get thirsty you have not drunk enough and you need to immediately increase your intake.


Little and often is important on longer rides and tours.  Ideally you should eat and drink a little every 20 minutes or so to maintain a steady supply of water and energy to the body.  If you go for a long time without eating or drinking and then cram lots down in one go your energy supply will have a similar pattern:  you will have patches where you feel really good and others were you feel really bad, corresponding to the levels of water and energy from food in your system.