Rear delts make for a complete physique...unfortunately, the rear delts can be a tough muscle to hit...bent-over lateral raises will hit them well in isolation and are useful to some degree. To really BUILD muscles, you need to use compound exercises.
Here's the problem...there ARE no compound exercises that directly target the rear delts specifically.
Shoulder presses utilize the rear delts to help stabilize the shoulder joint, not to actually press the weight up. The rear delts function to pull the humerus (the upper arm bone) posteriorly (to the back), not to raise it up in a vertical movement pattern - that's the front and side delts at work, along with the triceps.
Rowing and pull-up movements actually give you a more direct attack on the rear delts according to their actual function but the large powerful muscles of the back (like the lats, teres major and rhomboids) tend to take over, leaving the rear delts out in the cold.
That's where THIS exercise combination comes along...you're going to work two directly antagonistic exercises that each hit the rear delts...it's basically the only common denominator between the two compound exercises.
And yes, that means this combination is going to BLAST your rear delts extremely hard....everything else gets a rest at some point between the two exercises...the rear delts get ZERO rest.
This combination is done in what I like to call an "In-Set Superset." What that means is instead of doing a normal superset where you do a full set of exercise then immediately do a full set of the other exercise, you're going to alternate reps of each exercise...and these exercises must share a common position so that you can transition smoothly between the two with no break.
You'll see exactly what I'm talking about once I show you the exercise in action here.
You're going to be doing a kneeling barbell shoulder press alternated with a leg-assisted pull-up done using that same barbell.
This one is best done in the power rack. Kneel down in the rack and set the safety rails to just below shoulder height.
Set the racking hooks about 2 feet higher...try this with just the bar as a dry run so you get the heights right before you add weight.
Start with the bar on the rails next to the uprights of the rack and kneel down. Grab the bar with a moderate to wide grip. I usually use a bit inside my bench press grip for shoulder press.
Get the bar into the start position for the shoulder press (I'll give you the back and side views side-by-side here).
As you press up it's CRITICAL that you push your head forward underneath the bar. This is what activates the rear delts (albeit to stabilize the shoulder joint). Force those elbows back and get your head under the bar.
Once you've hit lockout, move the bar forward until it hits the uprights of the rack then set it down into the racking hooks. This is where you'll need to make any adjustments to the height of those hooks - you don't want it to be a stretch to get the bar up and in and but you also don't want them to be too low that you end up dropping the bar more than a few inches into them.
Now do the pull-up. Keep your toes on the ground and use your legs to guide and assist the movement so that you can use EXTREMELY strict form, pulling your elbows back as far as you can and pullling yourself up until the bar hits your upper chest.
This is VERY important as the higher you pull (to that point) and the more you can focus on pulling your elbows back, the harder the rear delts will be worked.
The toes on the ground are important to achieving that maximum range of motion and for taking up some of your bodyweight. If you get your feet off the ground, your bodyweight will result in the bigger muscles of the back kicking in too much, defeating the purpose of the exercise. Your toes on the ground also allows you to push your body forward as you pull your elbows back.
Lower yourself back down to your knees, get the bar off the racking hooks then lower back to the bottom of the shoulder press position. Don't set the bar back down on the rails...keep it at shoulder level when you start the next rep.
Repeat until your rear delts are basically screaming :). They will be the continuous link between these two exercises and will get worked HARD.
You'll feel them when you finish the set and you will feel them likely as you never have before starting over the next day or two.
This is a GREAT rear delt exercise that utilizes two compound movements to push that smaller muscle they have in common to the limit.
I've got a video of this technique in action, posted on YouTube here...if you're interested in seeing more insane exercises like this definitely subscribe to my channel!