Are there any studies on fat burning in performance cyclists?
Look at the work of Jeff Volek https://scholar.google.com/scholar?hl=en&amp;as_sdt=0%2C5&amp;q=Jeff+Volek&amp;btnG=
Rethinking fat as a fuel for endurance exercise  is one of his many papers, also Metabolic characteristics of keto-adapted ultra-endurance runners
He has also writen a book The Art and Science of Low Carbohydrate Performance
Low-carbohydrate diets for athletes: what evidence? Is likely to be cited by most recent papers.
These days most of his work is in Type2 diabetes, hence I dont' think he has published much on sport since his book.  Some of his sport research was done with static bikes using
professional long distance cycleists.
Ignore any research that had people on a low carb high fat diet for less then a few weeks before measuring performance as it is a common error other researchers make.