it's a good idea to have regular physical activity (even daily gardening is good). the human body has over 600 different muscles.

if you don't, your only other choice is to work out. otherwise, it is believed that starting at age 35, up to 70% of all your muscle will be lost by age 70.

don't wait around for medical science and your doctor to take care of everything for you!

this link shows major muscles on the left, and exercises with short videos on the right:

http://exrx.net/Lists/Directory.html