Okay, I see what you're getting at, but I'm not sure it's that important where the fatty acids (
FAs) are coming from. The body seems to do a good job of distributing FAs where it wants to--and transporting them to the bloodstream when needed.
Nor is it clear (to me) that
max. transport of subcutaneous FAs occurs at 25% of VO2max, only that most of the FAs at that level are coming from subcutaneous tissue. Maybe the transport continues at a high level or even goes higher, supplemented by the FAs stored in muscle. (Andy Coggan made a passing reference to this effect in a recent podcast, saying that at high heart rates, blood flow is shunted towards working muscles and away from subcutaneous tissue, thus reducing the transport of FAs into the bloodstream, but he didn't specify how high the heart rate needs to be to cause this shunting.)
The pertinent section of
the article:
At 25% VO2max, FAox [fatty acid oxidation] comprises >90% of energy expenditure and more specifically plasma FAs provide the largest energy contribution, where muscle glycogen and IMTG [intramuscular triglycerides] contribute very little. At exercise intensities <65% VO2max muscle glycogen and IMTG oxidation increase considerably to as much as 50% of energy expenditure
When approaching 65% of VO2max, since 50% of energy is coming from glycogen+IMTG, that presumes the other 50% is coming from somewhere else (subcutaneous FAs?).