Mike wrote-: "The point is that some "forearm" muscles are able to flex the forearm and some forearm muscles are able to extend the forearm. Those are the muscles that cross the elbow joint."
Mike is correct and I applaud his questioning comments. I shouldn't have been so didactic by making a general overarching statement about forearm muscles that is only generally true, but not absolutely true. I therefore need to qualify my statements with a more detailed explanation, which is always a good thing, because it promotes a better (more accurate) understanding.
Theoretically, it can be said that any foreram muscle that has its origin (or part of its origin) above the elbow joint can
assist in flexion or extension of the elbow joint depending on its position and muscle bulk - even though that forearm muscle may have another primary function (moving more distal joints).
I have therefore produced two photos.
The photos are too large to embed in this message, so I will provide links.
Photo 1 - Forearm Muscles -
http://perfectgolfswingreview.net/ForearmMuscles.jpg
Photo 2 - Origin and insertions of forearm muscles -
http://perfectgolfswingreview.net/Fo...lesOrigins.jpg
Take for example the aconeus muscle. It has its origin above the elbow joint and its insertion below the elbow joint. In that sense, it can be perceived to be an elbow extensor muscle. However, it is a comparatively tiny muscle relative to the triceps muscle and plays very little role in active elbow extension.
The same applies to the brachioradialis muscle. It has its origin above the elbow joint and its insertion near the wrist. It can definitely flex the elbow joint, but considering its relatively small bulk (compared to the biceps and brachialis muscles) and its far insertion point (which decreases leverage) it plays a far smaller role in elbow flexion that the upper arm muscles (biceps and brachialis muscles) which have great leverage because of their proximal forearm insertion points. Its main role is to produce a neutral forearm position when the forearm is extended in a non-neutral position (either supination or pronation) and the forearm is then flexed to a neutral position. It helps in rotating the forearm to a neutral position while
assisting the biceps muscle in flexing the elbow.
Yodas Luke suggested that extensor digitorum and extensor carpi ulnaris may assist in elbow extension. I don't think that's correct and the photos show why I disagree - note that the extensor carpi ulnaris and extensor digitorum muscles actually arise from an origin
below the elbow joint and its only their common extensor tendon that is attached to the humerus just above the elbow joint (at the lateral humeral epicondyle). They have very little leverage in extending the elbow joint - compared to the triceps muscle.
The extensor muscle that has its origin above the elbow joint is the long head of extensor carpi radialis, but its position and small bulk suggests that it has little role to play in elbow extension.
Look at the sheer size of the triceps muscle and the triceps tendon, and consider its advantageous point of insertion. You can then see why its the dominant muscle in elbow extension.
Jeff.
