What
people commonly refer to as the biceps are actually two distinct
muscles: the biceps brachii and the brachialis. Both muscles run
along the front of the upper arm, from the shoulder to the elbow.
The biceps brachii is responsible for the ball-like "head"
on your biceps; the brachalis is the larger of the two, located
underneath the biceps brachii. Both muscles that make up the biceps
help flex your elbow. In addition, the biceps brachii helps to supinate
your forearm. This is very helpful in swinging a racquet in sports
like racquetball and tennis.