You are using both muscle glycogen and fat. It isn’t one or the other, it is how much of each. Generally that is what people use all the time, the question is how much of each. The more you go from slow and easy to harder and more difficult, the more you move from fat to muscle glycogen.
To get a good idea, we would need to know what your heart rate is while swimming. And then there are some formulas that would give you an idea where you are on the scale.
This little picture helps to understand it:
And you can read all about it here:
I generally wait many hours after I have eaten lunch so there is no IOB, but before dinner.
I don’t have typical “days”. I try to exercise different heart rate zones throughout the week. So it is more likely for me to have a typical “week” rather than a typical “day”.
So I might have 1-2 long runs, a few runs with speed intervals, a few medium length runs, a few recovery runs. I try to hit all the different heart rate zones, from 1 (“this is easy, I can do this all day”) to 5 (“I’m about to die”).
Happy Anniversary! Have fun today!
