My understanding is that medial rotation of the upper arm , specifically, when the humerus is parallel to the body, is the action that best isolates* the pectoralis major muscles (as opposed to flexion or adduction).

 

Could someone please confirm or refute this.

 

Thank you.

 

*By 'isolation' I mean that the movement engages the smallest number of other muscle groups.

My understanding is that medial rotation of the upper arm , specifically, when the humerus is parallel to the body, is the action that best isolates* the pectoralis major muscles (as opposed to flexion or adduction).

 

Could someone please confirm or refute this.

 

Thank you.

 

*By 'isolation' I mean that the movement engages the smallest number of other muscle groups.

 

 

Muscles in isolation are bit academic - muscles work in groups and movements tend to rely on groups - but that said I am not sure about solely rotation explanation. Firstly P.Maj has two heads and is partly cruciate (fibre bundles cross) - thus the actions are never simple. You have adduction, rotation, flexion - and combinations. But the sternocostal and the clavicular heads can work antagonistically - so again complications.

The pectoralis major muscle is a large flat-shaped muscle covering the upper part of the chest. Its origin is from the sternum, shoulder girdle and the first six ribs. It inserts on the proximal end of the humerus. It forms the axilla's anterior wall and acts to adduct and flex the arm. The trapezius muscles are known for raising, retracting and rotating the scapula.

Thank you for your contributions.

 

I understand that I'm probably splitting hairs here and pure isolation is impossible and several muscle groups are involved. What I realy mean by that is that the "bulk" of work is done by a certain muscle group.

In the above example of Pec.Major:

-the flexion involves (not only but) primarily P.Major and Front Deltoids, with Deltoids carrying the "bulk" of the load;

-the adduction engages (not only but) primarily again P.Major and Lats, with, approximately equal sharing of the load between the two;

-the medial rotation with the humerus being parallel to the body engages primarily P.Major and Subscapularis, with the "bulk" of the work done by P.Major (e.g. if one bends the arm at the elbow joint to the side at a 90 degree angle and overcoming resistance turns it inward, the P.Major would carry most of the load).

 

Would you agree with that?

Edited November 12, 201411 yr by noma

I think I would hazard that anterior Deltoid would have a major part to play in med rot. Thinking aloud - LatDorsi comes from the back and attaches to front of humerus (very rough terms) it is a big muscle and with the arm parallel to the body would surely play a part in this movement.