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I t p a y s t o b e A B M P C e r t i f i e d : w w w. a b m p . c o m / g o / c e r t i f i e d c e n t r a l 87 NO MUSCLE IS AN ISLAND Now, let's go into the studio and see how the fi ve muscle roles—agonist, synergist, antagonist, neutralizer, and supporter—perform on the stage of the human body. We've chosen a straightforward scene that involves our actor reaching out to grasp a banana. Specifi cally, this focuses on fl exion of the right shoulder. As we'll see, however, no muscle is an island and even simple actions can prove to be complex. Playing the role of agonist, and producing the main action, will be the deltoid's anterior fi bers. The script instructs the arm to raise to a nearly horizontal level so the hand can reach the fruit (Image 5). Spanning from the clavicle to the humerus, the muscle belly is in place. This should be a cinch, as the anterior deltoid has done this countless times. One take, and it will be a wrap. Our director leads the scene: "'Grasp the Banana.' Take One. ACTION!" The anterior deltoid fi bers concentrically contract, but wait ... "No, no, CUT." What went wrong? Well, when the anterior deltoid fi bers engaged, instead of just raising the arm, the belly pulled both of its tendinous ends toward its center, which is exactly what a muscle will do when left to its own devices. So the clavicle depressed while the humerus barely lifted (Image 6). It looks as though our agonist will need some synergists to assist in producing this main action. For these roles, we've hired the biceps brachii, the clavicular portion of the pectoralis major, and the coracobrachialis. Our director resumes: "Here we go. Quiet on the set. ACTION." The deltoid contracts, the two synergists begin to hoist and ... "CUT." What's wrong now? Even with the efforts of these three strong muscles, they can barely lift the arm without the inhibition—or relaxation—of surrounding muscles (Image 7). "Bring in the antagonists! Now, listen up, posterior fi bers of the deltoid, latissimus dorsi, and teres major: your job is to relax and lengthen as the agonist and synergists pull the arm into fl exion. Got it? OK. Take Three and ACTION" (Image 8). Looking good, but ... "Hold it, HOLD IT. What's with all the scapular movement?" It turns out that the agonist (deltoid) and synergists (biceps, pectoralis major, etc.) produce so much pull on their "stable ends" that the scapula (and, by proxy, the clavicle) are being yanked up and over the shoulder. STORY 2 "I'm trying." 5 Take One: anterior deltoid engages. 7 Releasing the antagonists for fl exion to occur. 6 Without the help of some synergists, the clavicle depresses. 8 With the antagonists disengaged, the arm begins to move. Action!