They are two separate entities that are not interchangeable. Muscles are made up of long, spaghetti-like fibers, while fat cells are round receptacles that store fat. I have been exercising them as well as walking and am on a low-fat diet. This is not an unusual occurrence as we age. You most likely are losing weight in muscle mass but gaining weight in body fat.
Muscle weighs more than fat.
However, those sites you just mentioned are very common in women. You said you were exercising those areas. Keep up with your walking, perhaps increasing the intensity of your walk. You might want to check out your caloric intake. Thanks for writing.