So the first three exercises here are supposed to target all three heads, right? So Jeff implies ("we're going to start with exercises that are going to hit all three heads at once"). But he said in another video that in order to activate your rear delts, you need to push your elbows behind your back. It doesn't seem to be the case in those first options 🤔. The last of the three opening exercises actually seems to have that elbow-behind-your-back element somewhat, but Jeff says it doesn't target rear delts much. I don't understand! 🙈
Extension, abduction, and external rotation.
The posterior deltoid assists in three movement patterns of the shoulder: extension, abduction, and external rotation. The extent to which they function for shoulder abduction is highly dependent on the angle of extension, with greater angles of extension yielding greater activation during abduction. However, for shoulder extension and external rotation, the rear delt is the primary mover.
It isn't a matter of consciously activating your muscles. Just do the movement pattern the muscle is built to do, and your brain will handle the activation of the muscle to facilitate the movement. Movements like reverse flies and facepulls are good for hitting the rear delts because they both use extension and external rotation.
It’s pretty impossible not to activate the rear delt if your carrying out the bent over row , in fact the strength curve is more favorable, as the resistance tails off a bit on the completion of the movement , (the term is ‘insufficiency ‘ I believe when a muscle contracts to the point where no more movement is possible simply because it has no more room to contract . As might be the case with Bent over raises . The results after that is largely limited bu your DNA .