On 2008-01-22, Andrzej Rosa wrote:

During aerobic exercise, it is *more* efficient to burn *more* fat because
that means that you're burning less glycogen, and glycogen is much more
scarce than fat (you only have ~400gm of it and that only provides as much
energy as about 200gm fat)

That would be liver alone, AFAIR. Most of glycogen is stored in muscles
and it takes a while to burn it all.

I don't think so. We enough to cover about 2hrs of hard running -- that's
a bit over 2000 calories. That's where the "hitting the wall" theory came
from -- you don't have enough glycogen to run a marathon without using some
fat.

I remember reading about glycogen
depletion workouts (recent fad in some sport related training regimes)
and it took quite an effort to burn it all, plus some fasting too.

Fat isn't good fuel source for aerobic workouts, because it needs more
oxygen to use it.

Without qualification, it's hard to say whether it's a "good" fuel source for
aerobic workouts.

It's "good" in the sense that it's abundant, but "bad" in the sense that it
doesn't provide energy as quickly.

Any kind of speed work depends heavily on glycogen stores, because intensity
is key.

But at least for longer events (e.g. 2hrs+), it is advantageous to be able to
metabolise fat as quickly as possible, because fat is abundant whereas glycogen
is not.

IOW you get winded more easily and overall intensity
must go down (a lot).

This is fairly basic stuff -- any book on exercise physiology or endurance
training will discuss it.

I'm missing context too, so it could be that I write about unrelated
topic. Anyway, we have more than 400mg of glycogen and fat is bad fuel
for intense aerobic activity. Your body will use it, if it has no

If you're doing the exercise for any purpose besides competing in endurance
events, I'd agree.

People competing in endurance events can and should do base training to address
this.

Cheers,
--
Elflord