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The original was posted on /r/velo by /u/prescripti0n on 2023-09-25 00:51:58.
Recently I had two rides >100km with a similar average heart rate ~150 BPM but one had an IF factor of 0.56 and the other 0.76. Rides with an IF factor below 0.75 are generally considered as a recovery ride. Yet my heart rate of 150 BPM is solidly between Z2 and Z3 for me. As such, from a heart rate standpoint these would be closer to endurance/tempo rides.
Both rides had a similar Kj output and so I’m trying to understand how much I should be consuming in terms of calories or carbs using this data.
I typically eat about 60g/h, but based off my power data I range between 350-450Kj so that means I’m eating about 54-69% of that back in carbs.
A lot of information floating around recommend food intake based on
- % of Kj output or
- no. grams of carbs / hour.
Which one do I use?
Some recommend to replace 20-30% of Kj for Z2 rides or 50% for Z3 while others say you should eat x amount of carbs per hour. Surely a small rider eating 120g/h would be overeating compared to a large rider given they burn calories at a much higher rate.
I’m also a bit confused because at low intensities, only about 20-30% of carbs are being used for energy but at higher intensities it’s almost 100% carbs? Do I replace only those carbs that I am burning or also the fat amounts to replenish my glycogen stores?
Also when using power to determine fueling, would this not be affected by aerobic decoupling? The power output at the start of a long ride is rarely the same at equal heart rates by the end.
tldr; my question is how do I use the information I have to know how much I should be eating and not just blindly following a 120g/h rule if I won’t even be close to burning that amount?