Whatever that process is, in my training regimen and per basic fitness concepts, mild to moderate physical activity uses glycogen while "fat" is used for longer duration activity! Of course breathing adjusts accordingly based on elements of abdominal adiposity, degree of activty/fitness level realizing that metabolism is part of the equation. The more active you are the higher your metabolism and less active, the slower metabolism though a paradox exists based on nutrition and other factors. If you are less active then your subjective view of x activity (scale of perceived exertion (RPE) per fitness level and how hard you breathe would be a 6 (example only) BUT 3 months down the line it would decerase to a 3 since you have become more accustomed to the activity and your system is more able to burn 'fat'. NOTE: There are varying scales for RPE /Borg scale for perceived exertion
RPE link (one)
https://www.verywellfit.com/rating-of-p ... le-3119445Of course, we have to breathe and based on that, our metablism is affected