Ah, polyarticular or multi joint muscles or the muscles which cross more than one joint always overlie a series of jewellery ( monoarticular or one-joint muscle), each of which duplicates some single part of the overall function of the polyarticular muscle.
The significance of this phenomenon is that it is our contention that general postural ‘set’ is determined less by the superficial polyarticular muscles than by the deeper monoarticular ones which are too often ignored because they are ‘out of sight, out of mind’.
Now lets see some of these secrets:
1- Soleus ( monoarticular ) beneath Gastrocnemius ( polyarticular )
Two large muscles attach to the Achilles band: the soleus from the deep side, and the gastrocnemius from the superficial side.
2- Adductor magnus, short head of the biceps ( monoarticulars ) femoris beneath long head of the biceps femoris ( polyarticular )
Deep to the biceps femoris long head, which is crossing both hip and knee, lies an important and not so obvious set of monoarticulars. This underlying connection can sometimes provide the answer to recalcitrant hamstring shortness and limitations to hip flexion and hip-knee integration . The first of these two monoarticulars is the short head of the biceps, which starts from the same tendinous attachment at the head of the fibula as the long head and passes to the linea aspera about one-third of the way up the femur.
Here there is a fascial continuity with the middle section of the adductor magnus, which passes up beneath the rest of the biceps femoris to attach to the inferior aspect of the ischial ramus, just anterior to the hamstring attachments. The short head of the biceps component may be overactive in chronically flexed knees or with a laterally rotated tibia, while the adductor magnus component may contribute to a posteriorly tilted pelvis, or the inability of the hip joints to flex properly.
This would suggest, for instance, that an anterior tilt of the pelvis ( postural hip flexion ) would yield more to release in the pectineus and iliacus ( single-joint hip flexors ) than to release in the rectus femoris or sartorius.
4- Brachialis, coracobracialis and supinator ( monoarticulars ), biceps brachii (polyarticular)
The short head of the biceps runs down from the coracoid to the radial tuberosity, thus affecting three joints: the gleno-humeral joint, the humero-ulnar joint, and the radio-ulnar joint (the shoulder, elbow, and the spin of the lower arm). This biceps has a series of monoarticulars beneath it to help sort out its multiple functions.The coracobrachialis runs under the biceps from the coracoid process to the humerus, thus adducting the humerus. The brachialis runs from the humerus, next to the coracobrachialis attachment, down to the ulna, clearly flexing the elbow. Finally, the supinator runs from ulna to radius, supinating the forearm.
The practical point of this distinction is that postural ‘set’ is often more determined by the underlying monoarticulars than it is by the overlying polyarticular. Thus, while in extreme cases the biceps might have a role in chronic humeral adduction or elbow flexion, the therapist is far more likely to get results from addressing the underlying monoarticulars than from work on the biceps itself.
These are some of secrets which will help in opening our minds to think globally rather than locally.