Agonist muscles in weighted dislocates?

Hi guys

 

Biomechanically speaking, weighted dislocates appear to be quite complex, probably due to my incomplete knowledge of shoulder joint anatomy. I am familiar with the prime movers of the shoulder, as well as the rotator cuff muscles, but still I hope that someone can explain this to me, for curiosity's sake.

 

I get a tremendous stretch in the chest, biceps and brachialis from the weighted dislocates, so I figure that those are the antagonist muscles in the movement (I may be wrong). However, I'm having more trouble figuring out which muscles act as the agonists, particularly when the weight is raised from behind the back?

Shoulder Dislocates works the external/internal rotators of the shoulder.   When the bar is going backwards behind you, it stretches out the medial rotators (because you're going into external rotation.)  When the bar is going back to the starting position, it stretches out the external rotators. 

different grip (larger, closer) substantially decrease a muscles involvement. for example with IM 7-8 

-close grip : traps work during flexion, the external rotator work and posterior delts works on the rest of movement

-larger grips: possibility to isolate more the external rotator and posterior delts.

another variable that plays a role is where is the weight.

-straight bar

-wood bar with weight in between the hands.

the first one is more difficult leverage at the side that does not change as you close the grip and this tends to be harder or rotator cuff, so if during IM 7/8 you cannot lift a weighted bar with medium grip you have weak ext rotator muscles. on the other side if you use concentrated weight and you cannot lift it you have weak traps.

 

another factor is the prone, supine grip. depending on it you can activate more the posterior delts and the triceps.

 

For this reason and after about 1 years and half trying different situation i prefer use both 10 kg as a single bar and 10 kg in the centr of a wood bar when i have to do maintaining sets for previous mobility. 2 sets each one at the beginning. one helps the other one.

Thanks guys! No such thing as isolation training 

 

Edit: I think what confuses me, is trying to visualize what the internal and external rotators do when the arms are extended behind the back. When the arms are in front, the nomenclature is obvious: The external rotator rotates the arm away from the trunk, but when the arm is behind the centerline, the external rotator then pushes the lower arm towards the trunk.