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BRACHIORADIALIS—PRONATOR AND SUPINATOR The brachioradialis attaches from the lateral supracondylar ridge of the humerus (immediately proximal to the lateral epicondyle) to the styloid process of the radius (Image 2). Therefore, it crosses the elbow joint anteriorly and can flex the forearm at the elbow joint. But can it also pronate or supinate the forearm (at the radioulnar joints), or does it have no pronation/supination capability? The answer again is yes and yes, depending on the position of the forearm when the motion started. From anatomic position (Image 3A), which is a position of full supination, the brachioradialis can pronate the forearm, but only to a position that is approximately halfway between full supination and full pronation (Image 3B). Why? Because this is the position that brings the radial styloid as close as possible to the lateral supracondylar ridge of the humerus. After all, fundamentally, a muscle's joint action is its concentric contraction, which means that it shortens and brings the muscle's attachments as close to each other as possible. But if the forearm begins in a position of full pronation (Image 3C), then the brachioradialis would have the ability to supinate the forearm, once again to a position that is approximately halfway between full supination and full pronation, bringing the radial styloid as close as possible to its humeral attachment (Image 3B). So, the brachioradialis can be a pronator or it can be a supinator. Or, if the forearm were to start in the position that is approximately halfway between full supination and full pronation, then the brachioradialis would have no pronation/ supination capability at all. 86 m a s s a g e & b o d y w o r k m a r c h / a p r i l 2 0 1 8 3A 3B 3C Brachioradialis Brachialis Biceps brachii 2 Brachioradialis. 3A: From a position of full supination, the brachioradialis can pronate the forearm to a position that is approximately halfway between full supination and full pronation. 3B: The brachioradialis with the forearm halfway between full supination and full pronation. 3C: From a position of full pronation, the brachioradialis can supinate the forearm to a position that is approximately halfway between full supination and full pronation. Illustration by Giovanni Rimasti. Permission Joseph E. Muscolino. Anterior view of the right brachioradialis. Permission Joseph E. Muscolino, The Muscular System: The Skeletal Muscles of the Human Body, 4th ed. ( Elsevier, 2017).