Carb tolerance testing during workouts

Hi All,

I am busy training for IM Austria in July, and have recently completed a few 3 hour plus ride sessions on Saturday. During these rides I thought I would test my carb intake abilities. I jumped straight in to 90g\hour and have not seen any ill effect. However, I am now not sure if the tests are valid or not. Riding intensity was TR Endurance zone for each of these tests. During SS I easily took in 60g\hour, but these workouts were only for a maximum of 2 hours.

Is there a suggested protocol for testing carb tolerance during workouts? Im struggling to find any additional info on how to best test. Everyone says to test, but dont go into how the test should be performed.

Thanks for any advice.


Hey Shane,

I don’t have any specific protocol but when I was testing my nutrition for my first IM I did the following:

  • long rides at IM goal pace for ±5 hours : Tested varying carb intakes to see how I felt during and after. I did these fairly often
  • long brick workouts : I did 1 or two 4-5 hour rides at IM goal pace with an hour run off the bike to test the nutrition I took in during the bike

Unfortunately I didn’t do any real indoor testing rides as most of my long rides on the weekend were outdoors. I didn’t follow an exact protocol but would up the calorie intake on each subsequent ride until I found the level at which i felt best during and after the ride (and during my run)

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I’ve only ever had issues at “race pace” after 5+ hrs (marathon MTB). Long training rides (less than race pace intensity) have been fine.

For me, this makes it difficult to test nutrition strategies. Short rides don’t work. Long rides only work if they are hard pace. And I really only do these during races.

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So I was just listening to Podcast 186, and they actually cover this very topic :grin:

Short answer (for me) is to test at race intensity and higher which should help define intake limits.

Thanks for the responses!