Voted Best Answer
Feb 05, 2013 - 06:52 PM
Answering question on agonist/antagonist:
Every muscle can act as either an agonist or antagonist, depending on what movement you are focusing on at the joint.
All muscles have an origin on one bone and an insertion on another, usually across a joint, sometimes across two joints ex. biceps brachii: the short head from the coracoid process of scapula, the long head from supraglenoid tubercle of scapula. They insert on the proximal radius and ulna, crossing both the shoulder and the elbow joints.
So, they act to supinate the forearm and flex the elbow across the elbow joint (a hinge joint) and to weakly flex the shoulder across the shoulder joint (a ball and socket).
In the motion of a biceps curl, the biceps is an agonist
and the main antagonist is the triceps.
For the push up, or bench press, the tricep is acting as the agonist to extend the arm, and the biceps is one of the antagonists.
So it all depends on what motion you are referring to across that particular joint, whether it is flexion, extension, internal rotation, external rotation, adduction, or abduction
Here is a good link with animations of muscle attachments, functions, innervations and video animations of how they act
Enjoy and best of luck!