Fuel Type and Energy Availability Table Explained

The table on page 16 displays caloric values (see the word “calories” on the top row, after the words “fuel type and energy availability”).

How much glycogen is stored in muscle depends on the individual and this can be between 275 and 400 grams (the more muscle you have, the more glycogen you’ll be able to store). In the average, healthy, 70kg male adult, it’s been calculated that 300 grams of glycogen can be stored in muscles (which is the example provided in the table: 1,200 calories). Again, everyone is different – so this is just a guidance example.

Secondly, the amount of fat in muscles is listed as 350 calories in the table. Where does this number come from?

Let’s flip back to page 11. In there, you’ll find that a small amount of fat, about 300 to 400 grams, is stored in muscles – this is called intramuscular fat. If you multiply that times 9, you’ll find that we store between 2,700 and 3,600 calories in our intramuscular fat adipose tissue.

But the table says 350 calories of fat stored in muscle (and not 2,700 and 3,600 calories). Why is this?

Here’s what you need to remember: intramuscular fat includes not only ‘skeletal’ or ‘voluntary’ muscles (quads, hamstrings, biceps, etc.), but also ‘organ’ muscles (heart, tongue, diaphragm, etc.) and other ‘involuntary’ muscles (oesophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessel, arrector pili in the skin which controls the erection of body hair, etc).

You’ll see why we're making this distinction in a moment.

Now let’s move onto the table on page 16. This table is an example based on the Cahill formulas. In this table, the fat calories in muscle refer only to ‘skeletal’ muscle in a 70kg average male, with a potential energy availability of 350 calories (which equals 39 fat grams) of ‘skeletal’ intramuscular fat and, as a result, it does not include the fat calories in ‘organ’ or ‘involuntary’ muscles. Instead, the fat calories in ‘organ’ or ‘involuntary’ muscles are included in the ‘adipose tissue/fat’ axis in the table.

AUTHOR: Alex Ruani, Research Director

Updated on: 15/10/2026