The commonness and appearance of stomach issues while competing in endurance sport is a problematic one. It can easily turn an enjoyable brick session into an unpleasant one or put you in a sticky situation in your race. But there is light at the end of the tunnel!!
If we can understand the principles of how much and how often we can take on carbohydrate as well as the variables that can affect gastro-intestinal discomfort (GID), we can easily solve these issues.
Understanding the “why” for needing to take on carbohydrate is possibly the most important pillar the in foundation of whether you feel you “should” or “should not” eat.
Here we can easily see that by taking on carbohydrate one is able to maintain blood glucose levels and keep performing exercise for another hour over that of a non-carbohydrate placebo. The maintenance of blood glucose is what enables us to keep the intensity of exercise going especially past the 2-hour point.
So, if you’re going to be racing for while or out riding for longer than 2 hours then you eating on the bike is incredibly important and influential on your ability to perform and should be considered.
Knowing how much we can take on board during a race or per hour will be one of the most enlightening bits of information we can get.
The amount we take on during activity is dictated by three main things;
- Maximal Absorption rates
- Intensity of exercise
- Duration of exercise
Item No. 1 – comes first as it dictates the rest. There is a fixed amount of glucose and fructose we can absorb per and anything over this will start to wreak havoc for your stomach.
- Glucose – 1g/per min or 60g/per hour
- Fructose – 0.5g/per min or 30g/per hour
Individually the amount you can take of each is shown but they both use multiple transporters or trains if you will, to pass through the intestine wall, meaning we can combine the two and have up to 90g/ per hour.
Item No. 2 – The intensity of exercise determines two things; the first is the higher intensity the higher requirement for carbohydrate to be able to maintain performance output. This is because stored carbohydrate in the form of muscle glycogen is used at a faster rate. So we require a higher intake of carbohydrate to maintain blood glucose (60-90g/per hour). BUT it should be noted the higher the intensity the less blood flows to the stomach potentially increasing GID this is trainable though and
And finally, No. 3 – Duration also plays a big role with the requirement for carbohydrate being less so when exercise lasts less than an hour (like a crit race) but if looking at an Ironman ranging between the elite at 8/9 hours and the amateur at possibly around 16 hours then eating become massively more important.
I personally performed research into the frequency of carbohydrate between one big feed and 3 smaller feeds but overall performance was equivocal– some participants performed better or the same with no detriment. But we did see the trend of lower heart rate and rate of perceived exertion.
Off the back of this smaller feedings of 20g every 20minutes or 30g every 30minutes would be both convenient/manageable frequency to hit your target amounts
Variables you possibly hadn’t considered
Other factors that influence stomach issues are listed here and aren’t within the scope of this piece to elaborate on, so I will leave you with these until next time.
- Hydration status
- Fibre intake
- Dairy intake
- Fat intake