You
have to do cardio after lifting for fat loss because your glycogen is
low from the lifting, and that way you will burn more fat.

And now, the Truth:

First
off, this quote, "glycogen is low right after lifting" isn't always
true. If you just did an upper body workout, your legs are still full
of glycogen.

Glycogen is the stored form of
carbohydrates in our body (found in the muscles and liver). It is one
source of energy when you are doing strength training, interval
training, and aerobic training. Your glycogen levels go down after
exercise, but increase after you eat carbohydrates.

It's
incorrectly believed by many that strength training will use up all of
your glycogen and then you will only have fat to burn during slow,
steady, monotonous (& useless?) cardio. Well, there are a lot of
problems with that assumption as well.

First,
you'd have to exercise for at least 90 minutes at a slow, steady pace
to fully deplete your muscle glycogen. And even an advanced,
higher-volume strength training workout will only deplete your muscle
glycogen by about 50-70% (and that is only if you perform multiple
exercises and sets for one muscle group).

Second,
muscle glycogen only goes down in the muscles that are worked.
Therefore, if you only do upper body exercises, your leg muscles will
remain nearly full of glycogen.

Third, you
require glycogen in order to perform a hard interval or cardio training
session. If you truly were glycogen depleted, your workouts would
suffer.

The bottom line is that you are
better off performing strength training and interval training to lose
fat, and not worrying about being glycogen depleted.

Don't
get suckered into thinking that you have to worry about scientific
details. Unless you are a trainer, you have better things to occupy
your mind, I'm sure. Just stick with an efficient, effective workout
that gets you in and out of the gym in less than an hour.

No
need to stick around longer than that. Do your weights and then your
intervals. Or feel free to do your intervals on your off-day. It's
consistency, not timing, that matters.

Sincerely,

Craig Ballantyne, CSCS, MS
Author, Turbulence Training