It can not be guaranteed that only fat will be burned off. So if you are burning 500 calories a day and you are controlling your caloric intake, you can lose a pound in 7 days of exercise. Get plenty of fruit, vegetables and protein from low fat sources along with whole grains, cereals etc.
Cardiovascular activity has the potential to work a variety of muscles.
Getting more muscles involved not only increases caloric expenditure, but gets more body parts active. Strength training has been demonstrated over and over again to be a great tool to defend against the negative effects of aging, and improves metabolic efficiency in some situations. This is just one of the many informative articles available. Check our directory for a list.