In addition to my previous references to Alan Couzens and Dan Plews, an interesting article from Tim Reed about training 12 / 15h a week instead of 30h :
https://rpgcoaching.com/how-im-going-to-try-to-win-races-on-half-pro-training/
more specifically this part about increasing fat ox with limited training time :
Achieving metabolic flexibility without long training sessions will be tricky as nothing stimulates fat burning like being out there for a bloody long time. The Norwegians, Cam Brown and many other big milage trainers would never be categorised as ever doing low carb sessions, at least from what I hear and read. However, if youāre doing 40 + hours of training a week youāre doing a lot of long sessions, can never replace what youāre burning in carbs and will almost inevitably become a good fat burner regardless of diet.
So how do I improve my now fairly poor fat burning on 12 hours a week training? The answer is an approach Iām not a fan of for athletes doing 25 hours a week plus but tends to work really well on low volume. It includes a lot more carbohydrate deplete/fasted sessions (I can still take in calories from fats and to a lesser degree protein). The goal of training with less muscle glycogen available is it stimulates a greater production of ālipaseā, the enzyme that mobliises fats for fuel more quickly during shorter duration sessions. The other way Iāll do it is nearly always front loading my training day. Not only does this tend to help with better recovery at night but by pairing more sessions back to back the total duration of that training session will force my body to become more dependent on fats for the fuel the longer it goes on.
This explain why Gustav eat pizza in the morning (35h training per week) while I comfortably perform most of my training fasted (7h to 15h a week) with small carb (natural food, not gel) ingestion if long session (> 2h) ...