because that's how the body is built
If your speaking about your biceps, it's because they don't start and end on your arm. Bi (2) Ceps Brachii has 2 heads. One of which originates on the coracoid process of the scapula. Both heads cross the elbow and insert on the radius. Thus because muscle pulls bones closer together, creating flexion, or bending the elbow. Same goes for triceps. Three heads, the long head originating on the scapula the other two on the posterior humerus (back of the arm). They insert on the elbow. This allows for extension of the arm and straightening the arm after bending the elbow.
http://www.exrx.net/Muscles/TricepsBrachii.HTML
With muscles!
the muscles
Basically, All the muscles in your entire body can move.There's muscles that you can move on your own, and there's muscles that you can't.Nevertheless, these muscles that you can't move, move by itself.These muscles are called "The cardiac and smooth muscles.".Muscles that you are able to move on your own are "Skeletal muscles.".- Christofer Placencio, 01/31/13.
they move using there powerful leg and arm muscles
It means that you naturally move your arm with out thinking that your going to move it. There are two types of muscles; voluntary muscles and involuntary muscles. Voluntary muscles are muscles that you think about to move sometimes and involuntary muscles are muscles that you don't think about moving. An example of an involuntary muscle would be your heart and an example of a voluntary muscle would be your arm even though you don't really have to think about it when you move it.
triceps
Your arm muscles work by contracting and releasing to lift a mug of coffee to your lips. The muscles flex and contract to move your arm.
Yes. lol If you have an elbow or your arm isn't broken you can move it!
biceps and triceps
biceps and triceps respectively
The humerous is the upper arm bone. Its primary function is to support the arm muscles and allow the arm to move.
forearm and upper arm muscles.