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Glucose you, sir?

20:43 8th July 1999 by Bikemagic
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The sun is baking down threatening to melt your head off. You’re coming to the end of a long ride. You feel thirsty and hungry. For the last 5 miles you hang on to your bike praying to be put out of your agony by a wayward clay pigeon shooter. Obviously it doesn’t often get that hot in this country, but when it does you’d better be prepared.


This kind of agony can be limited to some extent with a little time taken thinking about what actually goes into your water bottle or camel back. As we examined in the last article, “To Drink or not To Drink” , maintaining a hydrated body is in simple terms a matter of matching the fluid that you loose during a ride with the fluid that you consume both during and after the ride. This is a tough task however when you consider that the body can only empty about 800 ml of water from the stomach each hour during a ride, and you may be loosing as much as 2 litres during this time.


As well as being hydrated on your ride you will also need to ensure an adequate supply of carbohydrate is available to tired legs. Unfortunately increasing the amount of carbohydrate in a drink has been shown to decrease the rate at which water can be made available by the body, reducing your performance on the bike.


In order to decide what to put in your bottle the first question you must ask yourself is what is my main priority. Hydration, refuelling of carbohydrate or a combination of the two.


The importance of replacing fluid obviously depends on the rate at which fluid levels are being lost from the body. This can depend on a number of factors such as the intensity and duration of the ride, the temperature on the day, the humidity and the individual rider concerned. Obviously on a really hot summer’s day with high humidity, fluid replacement becomes a greater concern than on a cool spring day.


What you decide to take with you on your ride should first of all taste good. If it tastes like the bottom of a cats litter tray you are unlikely to drink gallons of the stuff. Secondly, how fast can the fluid be passed through the stomach into the small intestine? This rate known as gastric emptying is all-important and determines the availability of fluid to the body.


Factors that effect the rate of gastric emptying include the concentration of carbohydrate in the drink. Increasing the amount of carbohydrate in a drink will increase the amount of fuel that you can supply to your body but will actually reduce the rate at which water can be made available. Research has shown that drinks with carbohydrate concentrations above 7 to 8% could reduce your ability to ride for long periods in the heat. If its cool however then fluid loss becomes less of a factor and a high % carbohydrate drink may be the choice.


It’s not a good idea to drink the entire contents of bottle in one go. Drinking 200-250ml of fluid every 15-20 minutes maximise the flow of fluid through the stomach.


You also need to take into account the number of particles in the solution. This is known as osmolality and it affects a drinks ability to be absorbed into your blood stream. Drinks with a high osmolality (Hypertonic) tend to draw water into the intestine causing discomfort, and should be avoided. Drinks that are isotonic have the same osmolality as the body fluids, leading to quick absorption into the blood stream.


All of this has probably confused you even further, but there are no simple answers. The trick is to know the environment in which you are riding and the type of rider you are. By thinking more carefully about what you put in your water bottle you may soon be popping the cork of a champagne bottle in race victory celebration.


 


SUMMARY


  1. Decide on your priority for the day. Avoiding dehydration or maintaining carbohydrate levels. Take into account the distance of the ride or race, the temperature, and humidity of the day.

  2. Look at the concentration of carbohydrate, the osmolality, and the taste of the drink.

  3. Practice with any new drink or drinking regime prior to competing in a race.

  4. Avoid salt tablets and strongly hypertonic drinks.

  5. Don’t wait to become thirsty to start drinking. Begin drinking early to anticipate sweat losses.

  6. Drink 200-250ml of fluid every 15-20 minutes.

 


©Andy Creigh July 3rd 1999