When you do not get enough nutrients from food, your blood glucose levels tend to fall, which triggers the release of the hormone epinephrine (adrenaline). Epinephrine is transported via the blood to the fat stores anywhere in the body, where it triggers the breakdown of fats (triglycerides) into fatty acids. Fatty acids leave the fat stores, enter the blood and are transported to any "hungry" muscle, where they are broken down to energy. (The Science Behind Fat Metabolism: Ketoschool)
So, the muscles don't just eat the nearby fat but the fat that is delivered to them via the blood from any part of the body.
Genetics affects where a person loses weight first, and it also depends on where they gain it first. (Dr. Janet Brill Medical Daily)
- Effects of Sit up Exercise Training on Adipose Cell Size and Adiposity (Tandofline)
- The effect of abdominal exercise on abdominal fat (PubMed)