The only way to really decrease muscle if you do indeed wish to do
so, is to stop using weights and strength training with the muscle
in question.
I will be honest with you when i say that if you are
a fairly young and fit individual, great decreases in muscle are
hard to achieve because even in the event that you do no weight
training at all with a certain muscle, your muscle has to atrophy
(get smaller) which is not a common or necessarily desirable thing
to have them do.
Atrophy is a natural decreasing in muscle size usually due to
extreme prolonged inactivity of that particular muscle.
Like I mentioned you can halt increases in your muscle tone
around your arm and even to some extent decrease the muscle
composition by just simply not working the arms when you do strength
training.
As for the body fat you mentioned around the neck and underarms, you
will need to do more effective fat burning type of cardio training.
All body fat is burned this way no matter where it is... And an
additional point for the backs of the arms is that you can do
certain exercises for that little area that I assume you're talking
about which is the back inner part of the arm close to the arm pit.
You can tone this area as you are burning your overall body fat
in order to get rid of that flabbiness your talking about there.
Lastly, nutrition is what ties it all together and makes sure you
are helping yourself from all aspects as opposed to canceling out
your gains by eating incorrectly.
As for what type of cardio format, what exercises to do, and how to
alter your nutritional habits, I would love to know more about you
and all of your fitness habits to better guide you on this matter.
Please feel free to check out my site and read about all that i can
offer you in regards to any further guidance you may need. Even a
structured program...
There is questionnaire you can fill out that will give me all
the info I need
JasonSpencer.askthetrainer.com I
hope to hear back from you!