Answer:
your biceps are the muscles that move your lower arm and hand up. You usually have two or more muscles for each bone. These muscles work together for instance the biceps and triceps. When your biceps contract, your arm bends up. when your bicep relaxes and your triceps contract, your hand lowers again, you can try it on a table. Lay your arm flat then raise your arm from the hand to your elbow, when you lift and let it down, you will se your muscles bulge.
Notice though that the muscles does not contract the other way or stretch. it relaxes.